Primary structure of the DNA polymerase I gene of an alpha-proteobacterium, Rhizobium leguminosarum, and comparison with other family a DNA polymerases

The structural gene for DNA polymerase I of Rhizobium leguminosarum was det ermined. The rhizobium DNA polymerase I consists of 1016 amino acid residue s with a calculated molecular weight of 111, 491 Dalton, The amino acid seq uence comparison with E. coli DNA polymerase I, Thermus aquaticus DNA polym erase I, and Rickettsia prowazekii DNA polymerase I showed that, although 5 '-nuclease and DNA polymerase domains are highly conserved, 3' to 5' exonuc lease domains are much less conserved. While both R. leguminosarum and R. p rowazekii belong to the alpha subdivision of the Proteobacteria on the basi s of 16S ribosomal RNA phylogeny, the primary structure of the DNA polymera se I is quite different; the rhizobium DNA polymerase I has 3' to 5' proofr eading exonuclease, but the rickettsia DNA polymerase I does not.