RETENTION OF REPLICATION FIDELITY BY A DNA-POLYMERASE FUNCTIONING IN A DISTANTLY RELATED ENVIRONMENT

The primary structures of the replicative DNA polymerases (gp43s) of b acteriophage T4 and its distant phylogenetic relative RB69 are diverge d, retaining only 61% identity and 74% similarity, Nevertheless, RB69 gp43 substitutes effectively for T4 gp43 in T4 DNA replication in vivo . We show here that RB69 gp43 replicates T4 genomes in vivo with a fid elity similar Co that achieved by T4 gp43. Furthermore, replication by RB69 gp43 in the distantly related environment does not enhance the m utator activities of mutations in T4 genes that encode other component s of the multienzyme DNA replicase, We also show that the fidelities o f RB69 gp43 and T4 gp43 are both high in vitro and that they are simil arly and sharply reduced ill vivo bg mutations that eliminate the 3'-e xonucleolytic proofreading function, We conclude that gp43 interaction s with the other replication proteins are probably nonessential for po lymerase fidelity.