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© 1999 Oxford University Press Human Molecular Genetics, 1999, Vol. 8, No. 9 1723–1728
A conserved nuclear element with a role in mammalian
gene regulation
Shaun R. Donnelly, Tim E. Hawkins and Stephen E. Moss
+
Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK
Received April 16, 1999; Revised and Accepted June 24, 1999
Mammalian genomes contain numerous fragments
of DNA that are derived from inactivated transposa-
ble elements. The accumulation and persistence of
these elements is generally attributed to transposase
activity rather than through possession or acquisi-
tion of a function of value to the host genome. Here
we describe such a repetitive element, named ALF
(for a
nnexin VI LINE-2 fragment), comprising 130 bp
of DNA derived from a LINE-2 sequence, which func-
tions as a potent T-cell-specific silencer. The expan-
sion of the DNA database arising as a result of the
human genome sequencing project enabled us to
identify ALF in,or close to, several well characterized
genes including those for annexin VI, interleukin-4
and protein kinase C-
β
ββ
β
. A systematic analysis of the
entire LINE-2 sequence revealed that ALF, and not
other regions of the LINE-2 sequence, was especially
highly represented in the human genome. Acquisi-
tion of a function by this repetitive element may
explain its abundance. These data show that a con-
served fragment of an interspersed nuclear element
has the potential to modulate gene expression, a dis-
covery that has broad implications for the way in
which we view so-called ‘junk’ DNA and our under-
standing of eukaryotic gene regulation.
INTRODUCTION
Eukaryotic gene transcription is largely under the control of
sequence-specific DNA-binding proteins that may act proxi-
mally or distally to transcription start sites. Most proteins of
this type have been reported to enhance or increase the rate of
transcription, but a significant number of transcriptional inhib-
itors or repressors have now also been described (1). Typical
gene promoters contain numerous binding sites for such posi-
tive and negative regulatory factors but, because the binding
sites are short, it is unusual to find extended regions of
sequence similarity between different promoters. The best
characterized conserved non-coding sequences are Alu
sequences and long interspersed nuclear elements (LINEs)
retrotransposons (2), both of which occur in abundance in
mammalian genomes.
In humans, Alu and mammalian-wide interspersed repeat
(MIR) sequences together with LINEs comprise >25% of the
entire genome (3). Of these three types of repetitive element,
LINEs are more closely associated with having a functional
role. A small proportion of LINEs are active, full-length and
have been reported to be capable of retrotransposition (4).
Recently, an extended MIR sequence was described known as
LINE-2 (3). In this study, we describe a LINE-2 fragment,
which commonly is located proximally to or within the introns
of many human genes. We have used the sequence from the
annexin VI (ANX6) promoter as a model to investigate the
function of this element and show that it is a potent T-cell-
specific silencer. These findings are consistent with the idea
that persistence of this element in mammalian evolution may
be because it has a function of value to the host genome, rather
than because of any intrinsic retrotransposase activity.
RESULTS AND DISCUSSION
We recently completed a functional analysis of the human ANX6
gene promoter (5). Extending this work, we found that the full-
length promoter was almost an order of magnitude weaker than
the minimal promoter in Jurkat T cells. This is in contrast to epi-
thelial and fibroblast lines, in which the full-length ANX6 pro-
moter has similar activity to the minimal active promoter. This
suggested that an element(s) located distally within the ANX6 pro-
moter might berepressive in T cells, butnot in other cell types. To
find out whether sequences in the ANX6 promoter were related to
sequences known to be involved in transcriptional silencing, we
used overlapping 200 bp fragments of the ANX6 promoter to
search the non-redundant nucleotide database at the NCBI using
BLAST. Unexpectedly, a region of the promoter extending from
bases –712 to –586 were similar to a large number (>100) of
sequences, all of which were identified using RepeatMasker
(http://ftp.genome.washington.edu/RM/RepeatMasker.html ) as
LINE-2 fragments. Six of these sequences were aligned with the
ANX6 sequence using MegAlign, and a consensus was derived in
which inclusive nucleotides are defined as those present in more
than half of the aligned sequences (Fig. 1a). The human and
bovineinterleukin-4(IL-4) sequencesbothconform to the consen-
sus, but the former was excluded to make the point that this ele-
ment is not restricted to the human genome. Note that the ANX6
sequence is 5' to 3' whereas the IL-4 sequence is reverse comple-
ment. Table 1 gives more information concerning the origins and
loci of theseelements, many of which are within introns of known
or hypothetical genes.
To find out whether other similar sized LINE-2 fragments
were represented at this level in the human genome, we used
+
To whom correspondence should be addressed. Tel: +44 171 380 7744; Fax: +44 171 413 8395; Email: s.moss@ucl.ac.uk
1724 Human Molecular Genetics, 1999, Vol. 8, No. 9
overlapping 150 bp regions extending over the entire LINE-2
sequence to search for homologous sequences (Fig. 1b). Most
of these 150 bp sequences were poorly represented, but the
region corresponding to the domain in the ANX6 promoter
occurred with high frequency. The 3' end of the LINE-2
sequence is an MIR that is already known to be an abundant
genomic element (3). The A
NX6 LINE-2 fragment (named
ALF) was found within or close to several well characterized
genes, including IL-4 and protein kinase C-β (PKC-β)
(Fig. 1c). Interestingly, the ANX6 and IL-4 genes are neigh-
bours within the cytokine gene cluster on chromosome 5q
(6,7). This may be coincidence, but the existence of conserved
regulatory elements within a cluster of genes may facilitate co-
ordinated regulation of gene expression during cell differentia-
tion or activation.
The conservation of ALF might be due either to preferential
transposition as an element in its own right, or to preferential
retention over surrounding LINE-2 sequence because it has a
property of some value to the host genome. Fortuitously,
orthologous ALFs were identified in the human and bovineIL-
4 genes so it was possible to test whether these ALFs, derived
from a common ancestral ALF, had diverged more or less than
Figure 1. Identification of ALF. (a) Alignment of bases –712 to –586 of the annexin VI promoter with six sequences retrieved from the nucleotide database. The
identities of the six sequences are given in Table 1. These six sequences are the closest matches of >50 related sequences extracted using BLAST on the non-
redundant nucleotide database at the NCBI. The shaded areas highlight nucleotides sharing identity in at least four of the seven sequences, from which the consen-
sus sequence is derived. Four sub-regions of particularly strong homology (HR1-HR4) are also indicated. (b) Frequency plot of LINE-2 fragments in the human
genome. The ~2.7 kb LINE-2 consensus sequence (http://www.girinst.org/~server/repbase.html ) represented 5' to 3' on the x-axis was divided into overlapping
150 bp sequences (overlap of 50 bp) and each sequence was used to search the non-redundant nucleotide database at the NCBI. The number of ‘hits’ is scoredon
the y-axis and the region corresponding to ALF is boxed in yellow. (c) Schematic representation of ALF in the ANX6, IL-4 and PKC-β genes (not to scale). Exons
are numbered and shown in green, and the relative position and orientation of ALF is indicated by the orange arrows. (d
–f) Diagon plot analysis of the orthologous
ALFs in the third intron of the human and bovine IL-4 genes. The human versus bovine comparison (d) shows that during evolution of the ancestral IL-4 intron 3,
ALF (as well as regions x and y) has been more highly conserved than its flanking sequences. In (e) and (f), comparisons of the human and bovine IL-4 intron 3
sequences, respectively, with the consensus LINE-2 sequence show that regions of LINE-2 homology extend 3' from ALF to y, and 5' to x and beyond.
Human Molecular Genetics, 1999, Vol. 8, No. 9 1725
neighbouring non-coding sequences. If surrounding non-
coding sequence shows similar levels of homology to ALF this
argues against preferential retention. Figure 1d shows a diagon
plot of these orthologous regions and reveals that ALF does in
fact stand out (together with regions x and y) as a conserved
sequence in this region of the IL-4 intron 3. Thus ALF, x and y
have been conserved in preference to surrounding sequences.
Further comparison of the human and bovine IL-4 ALFs with
the LINE-2 consensus (Fig. 1e and f) shows that ALF and an
extended region of surrounding sequences, including x and y,
are all of LINE-2 origin, suggesting that they represent the
remains of a complete ancestral LINE-2 element. It is interest-
ing to note that regions x and y also correspond to more highly
represented parts of the LINE-2 sequence as shown in Figure
1b. ALF thus did not enter the IL-4 gene as a repeating element
in its own right, but as part of a LINE-2 element. Therefore, a
LINE-2 element in the ancestral IL-4 gene has, during evolu-
tion to the human and bovine genes, preferentially retained
several conserved regions, of which ALF is one.
We then investigated the second possible reason for the
abundance of ALF, namely that ALF has a function that may
be useful to the host genome. In IL-4 and PKC-β,ALFwas
located some distance from the respective promoter and in
reverse and forward orientation, respectively (Fig. 1c). To test
whether ALF had genuine silencer activity, we cloned the
sequence into the pGL3-promoter, in forward and reverse ori-
entation, distally and proximally to the promoter (Fig. 2). In
both orientations and irrespective of distance from the pro-
moter, ALF virtually abolished the production of luciferase in
Jurkat cells, thereby satisfying the criteria for definition as a
silencer (1,8). However, in A431 and HeLa cells, ALF func-
tioned as both enhancer and silencer, depending on orientation,
position and cell type. In HeLa cells, ALFwas weakly active in
the forward orientation when proximal to the promoter, but had
strong enhancer activity (3- to 8-fold higher) in the reverse ori-
entation, whether distal or proximal to the promoter. In A431
cells, ALF functioned as a weak enhancer when proximal to
the promoter, but repressed transcriptional activity when
located distally to the promoter.
To gain further insight into the repressive activity observed
in T cells, we first examined a short but highly conserved 20
nucleotide domain (the HR1 domain in Fig. 1a) at the 5' end of
ALF. Deletion of this region, generating the construct ∆HR1-
Luc, substantially relieved the repressive activity observed in
Jurkat cells, particularly when cloned in the forward orienta-
tion (Fig. 3a). In A431 and HeLa cells, removal of HR1 led to
loss of enhancer activity. These data indicate that HR1 contrib-
utes to the dual role of ALF. However, the fact that ∆HR1-Luc
was still repressive in Jurkat cells indicates that HR1 is not
solely responsible for the silencer activity of ALF. The mecha-
nisms by which silencers suppress promoter activity are not
well understood, but they may act by directly interfering with
the basal transcription complex (9). This type of interaction
was suggested to underlie transcriptional repression exerted by
the silencer in the 3'-untranslated region of the IL-4 gene in
Th1 cells (10). Interestingly, although there was noevidence of
T-cell-specific transcription factors binding to the HR1
domain, we did find myc-associated zinc finger (MAZ) bind-
ing (11) to HR1 (data not shown) and, because MAZ binding
has been linked to DNA bending (12), it is possible that ALF
could function via a direct interaction with the basal transcrip-
tion complex. However, the MAZ-binding site is not present in
Table 1. Chromosomal location and characteristics of genes containing ALF
Sequence GenBank
accession no.
Region of homology % homology to
anxVI region
Source Comments
1 AC002398 33 237–33 108 50.8 Human Chr 19q13.1 Intron 6 of α-chimaerin homologue
2 AG000382 71–203 50.0 Human Chr 21q No further information available
3 U14159 889–764 52.4 Bos taurus Intron 3 of the IL-4 gene
4 AC004030 7388–7246 54.8 Human Chr 19p13.3 Intron 3 of an unknown hypothetical protein
5 AC002299 83 094–82 961 46.8 Human Chr 16p12 Intron 5 of the PKC-β gene
6 Z95113 72 854–72 721 52.4 Human Chr 22q11.2 Nearest identified EST 12 kb upstream
Figure 2. ALF is a T-cell-specific silencer. ALF was cloned into pGL3-
promoter in forward (F) and reverse (R) orientations, proximally and distally to
the promoter. Constructs were tested for activity in Jurkat, HeLa and A431
cells. For each data set, the activity of pGL3-promoter was set at 100%. Data
are the means of four (Jurkat) or six (HeLa and A431) independent transfec-
tions (±SEM) normalized by dot-blotting.
1726 Human Molecular Genetics, 1999, Vol. 8, No. 9
all ALF sequences, so this is unlikely to be an important mech-
anistic component of silencing by ALF.
Because IL-4 gene expression in T cells can be modulated by
phorbol ester and calcium ionophore (10,13–15), we performed
electrophoretic mobility shift assays (EMSAs) with HR1 compar-
ing nuclear extracts from control cells with those prepared from
cells exposed to these agonists for 2 h. The results in Figure 3b
show that HR1 forms a gel-shifted complex in activated Jurkat
cells that is absent in A431, HeLa or Daudi cells. Note that HR2
did not form specific gel-shifted complexes in similar experi-
ments, and HR3 and HR4 remain to be investigated. Figure 3c
shows that addition of cycloheximide to the cells at the same time
as the agonists inhibited induction of the HR1 complex, whereas
cyclosporin A had no effect. These results show that the induced
factor required de novo gene transcription and was not a resident
cytosolic transcription factor such as a STAT (signal transducer
and activator of transcription) or NF-AT (nuclear factor of acti-
vated T cells). To define the binding site for this factor more
closely, we searched the Transfac database (http://transfac.gbf.de/
cgi-bin/matSearch/matsearch.pl ) for known transcription factor-
binding sites. The only recognized sequence in this short domain,
CCCTCCC, corresponded to the MAZ-binding site (11). We then
investigated binding to a series of DNA oligomers with unitary
deletions in both the 5' and 3' directions and resolved the binding
site to the 12 nucleotide sequence, 5'-CTCCCACTCACT-3'.
Since this sequence does not correspond to the binding sitefor any
known transcription factor, binding may occur via a novel protein
induced by phorbol ester and ionophore. Finally, we investigated
the effects of phorbol ester and calcium ionophore on expression
of the endogenous ANX6 gene. The western blot in Figure 4a
shows that the level of annexin VI protein falls rapidly between 8
and 12 h afteraddition of theagonists. Annexin I, blotted usingthe
same extracts, maintained a constant level of expression during
the courseof theexperiment. These findingswere corroborated by
northern blotting (Fig. 4b), which showed that annexin VI mRNA
falls to barely detectable levels 12 h after the application of phor-
bol ester and calcium ionophore. Thus, like the IL-4 gene, which
also contains an HR1 sequence within ALF, ANX6 gene expres-
sion is down-regulated by phorbol ester and calcium ionophore in
Tcells.
In summary, we have identified a LINE-2 fragment named
ALF that is a potent T-cell-specific silencer. We also show that
agonists that down-regulate ALF-containing genes in T cells
induce a factor that binds to a sequence within ALF. These
findings are in contrast to other reports associating enhancer or
promoter activities with repetitive elements (16,17), because
ALF has the potential to function as a cell-type-specific
silencer. We favour the hypothesis that this is not an arbitrary
activity, and that ALF contributes to gene regulation in vivo.
This work thus supports the idea that fragments of a repetitive
element may be preserved preferentially within the host
genome during evolution if they take on a function that is
advantageous to the host.
MATERIALS AND METHODS
Materials
Tissue culture media and supplements were from Life Tech-
nologies. Western-Blue substrate, goat anti-rabbit alkaline phos-
phatase-conjugated antibody and the luciferase assay kit were
Figure 3. HR1 is a functional component of ALF. (a) To test the role of the first 20
nucleotides of ALF, a truncated ALF lacking this region (∆HR1-Luc) was cloned
in both forward (F) and reverse (R) orientations proximally to the SV40 promote
r
in the vector pGL3-promoter. Constructs were tested in Jurkat, HeLa and A431
cells, and results are shown comparing the activities of those with ALF-Luc (ALF
cloned into pGL3-promoter). Data are the means of four (Jurkat) or six (HeLa and
A431) independent transfections (±SEM) normalized by dot-blotting. (b)HR1
forms a gel-shifted complex with an inducible factor in Jurkat cells. EMSAs were
performed in which nuclear extracts from control or PMA/A23187 (P/A)-stimu-
lated cells were mixed with
32
P-labelled HR1. The P/A-inducible band (labelled
‘Induced band’) appears only in Jurkat extracts. (c) EMSAs showing that the P/A-
inducible band is inhibited by cycloheximide but not by cyclosporin A. Nuclea
r
extracts were prepared from control and P/A-stimulated (*) Jurkat cells cultured in
the presence or absence of cycloheximide or cyclosporin A.
Human Molecular Genetics, 1999, Vol. 8, No. 9 1727
from Promega. [γ-
32
P]ATP (3000 Ci/mmol) and [α-
32
P]dCTP
(3000 Ci/mmol) were from Dupont-NEN. DNA oligomers were
from Life Technologies. Hybond-N membrane was from Amer-
sham and Immobilon-P membrane was from Millipore. All other
chemicals were obtained from Sigma. pGL3-basic and pGL3-
promoter luciferase vectors were from Promega. TA cloning vec-
tor was from Invitrogen. pTAG cloning vector was from R&D
Systems. Taq DNA polymerase, restriction endonucleases and all
other DNA-modifying enzymes were purchased from Promega.
HeLa and Daudi cells were generously provided by Dr Mark
Marsh (University College London) and the human β-actin cDNA
was a gift from Dr David Flavell (University College London).
Annexin VI promoter constructs
The deletion series of the ANX6 promoter in pGL3-basic has been
described elsewhere (5). The 126 bp repetitive element was ampli-
fied by PCR using the oligonucleotides 5'-CTCCCTCCCACT-
CACTCC-3' and 5'-TACCTGCGGAAAGTGTTC-3' as upstream
and downstream primers, respectively, with the ANX6 promoter as
template (18). The first of these primers (annealed to its comple-
mentary strand) was also used as the HR1 oligo in gel shift assays
(see later). The PCR product was subcloned in forward and reverse
orientationsinto pGL3-promoter, bothproximally and distally(3 kb
upstream) to the SV40 promoter. To test the function of the most 5'
region, the ∆HR1 construct was made in an identical fashion but
with the oligonucleotide 5'-TCCAGCCACACTGGCCC-3' as
upstream primer. In this case, the PCR product was subcloned into
pGL3-promoter in forward and reverse orientations proximally to
the SV40 promoter. All constructs were verified by DNA sequen-
cing.
Cell culture and transfections
A431 and HeLa cells were cultured and transfected as
described previously (5). Jurkat and Daudi cells were cultured
in RPMI containing 10% heat-inactivated fetal calf serum, 25
mM
L-glutamine, 100 U/ml penicillin and 100 µg/ml strepto-
mycin sulfate. Jurkat cells were transfected by electroporation
using a GenePulser II electroporator (Bio-Rad). A total of 10
7
cells were harvested per transfection, pelleted at 1200 r.p.m.
for 5 min at room temperature and washed once in electropora-
tion buffer (0.2 M HEPES pH 7.4, 0.14 M NaCl, 0.15 M KCl,
7 × 10
–4
MNa
2
HPO
4
,6× 10
–3
M glucose). Cells were then
resuspended in 10 ml of electroporation buffer and pelleted
again, before being resuspended in 250 µl of electroporation
buffer. DNA (25 µg) was added and the cells were transferred
to 4 mm electroporation cuvettes (Bio-Rad). Electroporation
was performed at 400 V, 125 µFand∞Ω. Cells were allowed
to recover for 5 min at room temperature and then transferred
into 10 ml of complete growth medium. Luciferase activity
was measured as described previously (5).
Dot-blotting was performed as described previously (5).
EMSAs were performed as described elsewhere (5,19) using con-
trol cells or cells that had been stimulated with 100 ng/ml phorbol
12-myristate 13-acetate and 1 µM A23187. Unlabelled double-
stranded HR1 oligonucleotide(5'-CTCCCTCCCACTCACTC-3')
and HR2 oligonucleotide (5'-TCCAGCCACACTGGCCCCC-
CTGCTG-3') were used as competitor and non-competitor,
respectively. Cycloheximide and cyclosporin A were used at con-
centrations of 10 and 500 ng/ml, respectively. Northern and west-
ern blotting were as described previously (5).
ABBREVIATIONS
ALF, annexin VI LINE-2 fragment; IL-4, interleukin-4; LINE,
long interspersed nuclear element; PKC, protein kinase C.
ACKNOWLEDGEMENTS
This work was supported by the Arthritis Research Council,
the Wellcome Trust, the Medical Research Council and Glaxo-
Wellcome.
REFERENCES
1. Ogbourne, S. and Antalis, T.M. (1998) Transcriptional control and the role of
silencers in transcriptional regulation in eukaryotes. Biochem. J., 331, 1–14.
2. Hwu, H.R., Roberts, J.W., Davidson, E.H. and Britten, R.J. (1986) Inser-
tion and/or deletion of many repeated DNA sequences in human and
higher ape evolution. Proc. Natl Acad. Sci. USA, 83, 3875–3879.
3. Smit, A.F.A. (1996) The origin of interspersed repeats in the human
genome. Curr. Opin. Genet. Dev., 6, 743–748.
4. Sassaman, D.M., Dombroski, B.S., Moran, J.V., Kimberland, M.L., Nass,
T.P., DeBerardinis, R.J., Gabriel, A., Swergold, G.D. and Kazazian,
H.H.Jr (1997) Many human L1 elements are capable of retrotransposition.
Nature Genet., 16, 37–43.
5. Donnelly, S.R. and Moss, S.E. (1998) Functional analysis of the human
annexin I and VI gene promoters. Biochem. J., 332, 681–687.
6. Davies, A.A., Moss, S.E., Crompton, M.R., Jones, T.A., Spurr, N.K.,
Sheer, D., Kozak, C. and Crumpton, M.J. (1989) The gene coding for the
p68 calcium-binding protein is localised to bands q32-q34 of human chro-
mosome 5, and to mouse chromosome 11. Hum. Genet., 82, 234–238.
7. Dolganov, G., Bort, S., Lovett, M., Burr, J., Schubert, L., Short, D.,
McGurn, M., Gibson, C. and Lewis, D.B. (1996) Coexpression of the
interleukin-13 and interleukin-4 genes correlates with their physical link-
age in the cytokine gene cluster on human chromosome 5q23-31. Blood,
87, 3316–3326.
8. Brand, A.H., Breeden, L., Abraham, L., Sternglanz, R. and Nasmyth, K.
(1985) Characterization of a ‘silencer’ in yeast: a DNA sequence with
properties opposite to those of a transcriptional enhancer. Cell, 41, 41–48.
9. Johnson, A.D. (1995) The price of repression. Cell, 81, 655–658.
Figure 4. Annexin VI is down-regulated by PMA and A23187 in Jurkat cells.
(a) Western blot showing annexin VI (Anx VI) and annexin I (Anx I) in lysates
of Jurkat cells cultured in the presence of PMA/A23187 (P/A) for 24 h. Sam-
ples were resolved by SDS–PAGE, transferred to PVDF and the top half of the
blot was probed for annexin VI and the bottom half for annexin I. Protein
bands were visualized after incubation with goat anti-rabbit alkaline phos-
phatase antibody using Western-Blue. Notice the sharp drop in annexin VI lev-
els at 12 h. (b) Northern blot showing annexin VI mRNA levels in Jurkat cells
over 12 h in P/A. The blot was stripped and re-probed for β-actin. Bands were
detected using a Fuji phosphorimager with MacBas software.
1728 Human Molecular Genetics, 1999, Vol. 8, No. 9
10. Kubo, M., Ransom, J., Webb, D., Hashimoto, Y., Tada, T. and Nakayama,
T. (1997) T-cell subset-specific expression of the IL-4 gene is regulated
by a silencer element and STAT6. EMBO J., 16, 4007–4020.
11. Bossone, S., Asselin, C., Patel, A. and Marcu, K. (1992) MAZ, a zinc-
finger protein, binds to c-myc and C2 gene sequences regulating transcrip-
tional initiation and termination. Proc. Natl Acad. Sci. USA, 89, 7452–
7456.
12. Ashfield, R., Patel, A., Bossone, S., Brown, H., Campbell, R., Marcu, K.
and Proudfoot, N. (1994) MAZ-dependent termination between closely
spaced human complement genes. EMBO J., 13, 5656–5667.
13. Andersson, J., Skansen-Saphir, U., Sparrelid, E. and Andersson, U. (1996)
Intravenous immune globulin affects cytokine production in T lympho-
cytes and monocytes/macrophages. Clin.Exp.Immunol., 104, 10–20.
14. Li-Weber, M., Salgame, P., Hu, C., Davydov, I. and Krammer, P. (1997)
Differential interaction of nuclear factors with the PRE-1 enhancer ele-
ment of the human IL-4 promoter in different T cell subsets. J. Immunol.,
158, 1194–1200.
15. Yanagihara, Y., Kajiwara, K., Basaki, Y., Ikizawa, K., Akiyama, K. and
Saito, H. (1997) Induction of human IgE synthesis in B cells by a
basophilic cell line, KU812. Clin. Exp. Immunol., 108, 295–301.
16. Piedrafita, F.J., Molander, R.B., Vansant, G., Orlova, E.A., Pfahl, M. and
Reynolds, W.F. (1996) An Alu element in the myeloperoxidase promoter
contains a composite SP1-thyroid hormone-retinoic acid response ele-
ment. J. Biol. Chem., 271, 14412–14420.
17. Yang, Z., Boffelli, D., Boonmark, N., Schwartz, K. and Lawn, R. (1998)
Apolipoprotein(a) gene enhancer resides within a LINE element. J. Biol.
Chem., 273, 891–897.
18. Smith, P.D., Davies, A., Crumpton, M.J. and Moss, S.E. (1994) Structure
of the human annexin VI gene. Proc. Natl Acad. Sci. USA, 91, 2713–2717.
19. Andrews, N.C. and Faller, D.V. (1991) A rapid micropreparation tech-
nique for extraction of DNA-binding proteins from limiting numbers of
mammalian cells. Nucleic Acids Res., 19, 2499.
