Dual Role of Gene D5 in the Development of Bacteriophage T5

Abstract

THREE distinct classes of phage-specific proteins—“pre-early”, “early” and “late”—are synthesised in a temporal sequence after infection of Escherichia coli with bacteriophage T5¹ (Fig. 2a). The synthesis of pre-early proteins begins within the first minute after infection and is shut off 8–10 min later^1,2. The beginning of synthesis of early proteins is delayed until about 6 min after infection. This delay is mechanical, and is a result of the transfer of phage DNA to the host cell in two steps^1,3. The rate of synthesis of early proteins decreases considerably after 20 to 25 min of infection, but synthesis does continue through the late period at diminishing rates. We have observed that the rate of synthesis of most early proteins is diminished normally even when the turn-on of synthesis of late proteins is defective⁴. This observation suggested to us the presence of a negative control mechanism for the ‘shut-off’ of synthesis of early proteins, rather than a passive shut-off, such as a competition between early and late transcripts for the translational system of the infected cell. We have identified a gene the product of which is required for the shut-off of synthesis of phage specific early proteins, but which is also required for the replication of phage DNA.