Characterization of the gene coding for the Rickettsia prowazekii DNA primase analogue

The gene (dnaG) coding for DNA primase in the obligate intracellular parasitic bacterium, Rickettsia prowazekii, has been isolated and characterized. An open reading frame (ORF) of 1848 bp capable of encoding 616 amino acids (aa) is located 18 bp upstream from the gene coding for the major sigma factor of R. prowazekii, sigma 73. Based on aa sequence comparisons of DNA primase from R. prowazekii, Escherichia coli, Salmonella typhimurium and Bacillus subtilis, we propose that R. prowazekii dnaG begins 69 bp into the ORF and encodes 593 aa with a calculated M(r) of 68,683. An upstream ORF overlaps 66 of the first 69 bp of the larger R. prowazekii dnaG ORF, suggesting either an overlapping gene structure or the generation of the smaller protein product of 593 aa. Predicted aa sequence of R. prowazekii primase compared to E. coli, S. typhimurium and B. subtilis primases reveals 30.5%, 30.5% and 29.7% aa identity, respectively. The R. prowazekii dnaG gene failed to complement an E. coli dnaG temperature sensitive mutation perhaps due to poor expression of the gene or inability to function properly in E. coli. The gene organization of an ORF followed by DNA primase (dnaG) and then the major sigma factor (rpoD) is consistent with the major macromolecular synthesis operons of E. coli, S. typhimurium and B. subtilis.