DNA polymerase of bacteriophage T4 is an autogenous translational repressor

In bacteriophage T4 the protein product of gene 43 (gp43) is a multifunctional DNA polymerase that is essential for replication of the phage genome. The protein harbors DNA-binding, deoxyribonucleotide-binding, DNA-synthesizing (polymerase) and 3'-exonucleolytic (editing) activities as well as a capacity to interact with several other T4-induced replication enzymes. In addition, the T4 gp43 is a repressor of its own synthesis in vivo. We show here that this protein is an autogenous repressor of translation, and we have localized its RNA-binding sequence (translational operator) to the translation initiation domain of gene 43 mRNA. This mechanism for regulation of T4 DNA polymerase expression underscores the ubiquity of translational repression in the control of T4 DNA replication. Many T4 DNA polymerase accessory proteins and nucleotide biosynthesis enzymes are regulated by the phage-induced translational repressor regA, while the T4 single-stranded DNA-binding protein (T4 gp32) is, like gp43, autogenously regulated at the translational level.