ROLE OF THE ACIDIC CARBOXYL-TERMINAL DOMAIN OF THE SINGLE-STRANDED DNA-BINDING PROTEIN OF BACTERIOPHAGE-T7 IN SPECIFIC PROTEIN-PROTEIN INTERACTIONS

The gene 2.5 single-stranded DNA (ssDNA) binding protein of bacterioph age T7 is essential for T7 DNA replication and recombination, Earlier studies have shown that the COOH-terminal 21 amino acids of the gene 2 .5 protein are essential for specific protein-protein interaction with T7 DNA polymerase and T7 DNA helicase/ primase, A truncated gene 2.5 protein, in which the acidic COOH-terminal 21 amino acid residues are deleted no longer supports T7 growth, forms dimers, or interacts with either T7 DNA polymerase or T7 helicase/primase in vitro. The single-s tranded DNA-binding protein encoded by Escherichia coli (SSB protein) and phage T4 (gene 32 protein) also have acidic COOH-terminal domains, but neither protein can substitute for T7 gene 2.5 protein in vivo. T o determine if the specificity for the protein-protein interaction inv olving gene 2.5 protein resides in its COOH terminus, we replaced the COOH-terminal region of the gene 2.5 protein with the COOH-terminal re gion from either E. coil SSB protein or T4 gene 32 protein, Both of th e two chimeric proteins can substitute for T7 gene 2.5 protein to supp ort the growth of phage T7, The two chimeric proteins, like gene 2.5 p rotein, form dimers and interact with T7 DNA polymerase and helicase/p rimase to stimulate their activities, In contrast, chimeric proteins i n which the COOH terminus of T7 gene 2.5 protein replaced the COOH ter minus of E. coil SSB protein or T4 gene 32 protein cannot support the growth of phage T7, We conclude that an acidic COOH terminus of the ge ne 2.5 protein is essential for protein-protein interaction, but it al one cannot account for the specificity of the interaction.