S Brenner's research while affiliated with MRC Laboratory of Molecular Biology and other places

... That "appendix" was eventually published as a mammoth 73 page paper that appeared in 1967, including many more rII mutants that Brenner and Barnett had mapped in the meantime [42]. And indeed, all of the weird exceptions, barriers and all, were explained there in mind-numbing detail. ...

... Up until this point, chemical mutagens had transformed one base into another, but acridine dyes could apparently either add or subtract bases -this novel feature was to prove decisive in what followed. In a brief paper written the previous autumn, Crick and Brenner, along with their colleague Leslie Orgel and his wife Alice Orgel, a PhD student, argued that deleting or adding a single base using an acridine dye would alter how the genetic information was read [20]. It could potentially render the message after the mutation non-sensical because what they eventually termed the "reading frame" (they initially called such mutations "phaseshift" mutants) would now be altered. ...

... Late in the infection of E. coli by phage T4, most of the protein molecules synthesized are the 'head protein', which ultimately encapsulates the phage DNA and so dominates the pattern of proteins made late in phage infection. Anand Sarabhai, Tony Stretton, Antoinette Bolle and Sydney took advantage of this to study the products of different T4 phage bearing amber mutations in their head protein genes (7). They discovered that, when such a T4 mutant phage infects a non-permissive E. coli host, only a fragment of the head protein is made. ...

... Furthermore, the amber suppressors are usually highly efficient, so that up to 70% of the amount of the wild-type protein can be produced. UAA (ochre) non-sense mutants and their suppressors were then rapidly identified [11]. In contrast to amber suppressors, ochre suppressors are much less efficient, and ochre mutants cannot be isolated in genes expressed in high amounts, such as phage structural genes. ...

... The T4 bacteriophage amber mutants were nonfunctional in wild-type (WT) bacteria strains, but phage function was restored by strains of bacteria carrying "amber suppressor genes" (Epstein et al., 2012). The observation that the nonsense codon introduced by the amber mutation resulted in polypeptide chain termination (Sarabhai et al., 1964), followed by careful reversion of mutant phenotypes with chemical mutagens, revealed that the "amber" mutants contained the UAG triplet. Later work showed that the "ochre" (following the color-based naming convention) mutants contain the UAA triplet and that "nonsense" codons were more appropriately named "chain termination codons" (Brenner et al., 1965). ...

... 1961 was a magic time at the LMB. That was the year that Sydney, together with his research student Alice Orgel, had worked on acridine mutagenesis, and had come to the conclusion that the mechanism was totally different from that of previous mutagens, like 5-bromouracil, that induced base substitutions and therefore discrete amino acid exchanges in the encoded protein (Orgel & Brenner, 1961). Acridines intercalate between base pairs in DNA and produce shifts in the reading frame. ...

... We used a STOP codon reversion assay to specifically probe for dA→dG changes caused by MutaT7 A→G and eMutaT7 A→G . In E. coli, the presence of a premature nonsense codon (TAG, TAA or TGA) within a protein coding sequence generally results in translation termination, and thus the production of truncated, functionally compromised protein products (52). Therefore, STOP codons placed in the middle of antibiotic resistance markers result in antibiotic-sensitive phenotypes. ...

... Lysates were made on CR63 (Signer et al. 1965) or Bb {Karam and Barker 1971). As shown inTable 5, the recombinant deletion that is scored in crosses has an in-frame amber mutation. ...

... These latter mutations often involve an alteration in a nucleotide pair not involved in the original mutational event. Figure 3 presents a compilation of the mutational changes found in several bacterial systems (Weigert et al., 1966(Weigert et al., , 1967Sarabhai and Brenner, 1967; and in yeast (Sherman et al., 1970). These studies contributed to deduction of the in vivo genetic code and, today, lend caution in analyses of the action of chemical mutagens in cases where protein primary structure is not examined. ...

... I went on to show that when H36 was reverted by 4-amino purine, a mutagen that induces transitions, the mutant site now encoded either glutamine or tryptophan (the tryptophan revertant is temperature-sensitive) (Stretton, Kaplan, & Brenner, 1966). Spontaneous revertants generated tyrosine at the amber site (Stretton & Brenner, 1967). By now, much of the code had been solved, and the codons for most amino acids were known (or at least strongly predicted-the 'pure code' folks were hard to convince of the accuracy of translation of synthetic polynucleotides in cell-free systems). ...