Regulation of the synthesis of the T4 DNA polymerase (gene 43)

Abstract

The product of T4 gene 43, DNA polymerase (P43), regulates the level of its own synthesis. Normally, the rate of P43 synthesis declines rapidly 10 min after infection. However, P43 synthesis can be induced late in infection by shifting cells infected with temperature sensitive mutants of P43 from 30 to 42° ( Russel, 1973). Studies reported here show that induction of P43 synthesis late in infection also occurs after shifting several different amber or temperature sensitive T4 mutant-infected cells from 30 to 42°; the mutations causing the effect are in T4 genes essential for DNA replication. This turn on can be 5- to 10-fold greater than the level of P43 synthesis during comparable wild-type infections. In addition to P43, several other proteins, including P41, are turned on in these experiments. Other observations relevant to this phenomenon are as follows. First, blocking DNA synthesis with chemical inhibitors does not enhance the rate of P43 synthesis. Second, the increased expression of P43 after the temperature shift is dependent on new RNA synthesis; i.e., the increased expression is blocked by the addition of rifampicin and does not occur when the host cell RNA polymerase is temperature sensitive or when the infecting phage contains a tsG1 mutation in the T4 mot locus, thought to be necessary for normal P43 synthesis. Furthermore, hybridization studies of labeled T4 mRNA with plasmid DNA (pVH18), containing the middle one-third of gene 43, show that new P43 mRNA is made when the increased expression of P43 occurs. Third, unlike the expression of P32, the increased expression of P43 is not affected by the absence of P46-mediated gaps in replicative DNA. Fourth, studies examining the stability of P43 under a variety of conditions indicate that P43 is not degraded at 42°. Several models of the control of gene 43 expression are discussed.