When complete transfer of DNA from phage T5 to Escherichia coli F is allowed, the induction of three classes of proteins can be revealed kinetically by means of pulse-labeling, disc electrophoresis, and autoradiography. At 37° T5 proteins of Class I are synthesized from about 1 to 5 min after protein synthesis is first allowed following infection. Synthesis of Class II proteins, which include the
... [Show full abstract] early enzymes, occurs during the 5- to 20-min period after initiation of protein synthesis. T5 proteins of Class III, among which are certain phage structural components, are synthesized from about 14 min until lysis at 45 to 60 min. When only the initial 8% section of T5 DNA is permitted to enter host cells, proteins of Class I can be synthesized but not proteins of Class II or III. The 8% section not only induces the synthesis of Class I proteins but also directs the “shutoff” of their synthesis as well as the shutoff of the synthesis of host proteins at the expected time. The initiation of the synthesis of Class II proteins depends on the prior formation of Class I proteins. It is therefore proposed that one or more of the Class I proteins exerts an active regulatory role in this shift of the synthesis from one class of proteins to another. Class I proteins are not precursors of Class II or III proteins and their period of synthesis can be extended by irradiation of the free phage prior to infection. They are therefore considered to be a new distinct class, which are probably coded for by the initial 8% section of the phage T5 genome.