Divergence of a DNA Replication Gene Cluster in the T4-Related Bacteriophage RB69

摘要: The genomes of bacteriophages T4 and RB69 are phylogenetically related but diverge in nucleotide sequence at many loci incompatible with each other vivo. We describe here the biological implications divergence a genomic segment that encodes four essential DNA replication proteins: gp45 (sliding clamp), gp44/62 complex (clamp loader), gp46 (a recombination protein). have cloned, sequenced, expressed several overlapping segments gene 46-45.2- ( rpbA ) -45-44-62 cluster compared its features to those homologous from T4. deduced primary structures all proteins gp45.2 this very similar (80 95% similarity) their respective homologs. In contrast, region (which nonessential protein T4) is highly diverged (∼49% between two phage does not encode RB69. Expression studies patterns high intercistronic sequences suggest evolved transcriptional translational control strategies for cistrons contained therein, different specificities. plasmid-phage complementation assays, we show posttranslationally, homologs can be effectively exchanged replicase assemblies; however, also results which mixed clamp loader complexes consisting gp62 gp44 subunits active replication. Thus, specificity gp44-gp62 interaction marks point departure systems.