A 29.5 kda outer membrane protein (OmpB) of R. prowazekii virulent Breinl strain is known to differ from its counterpart in attenuated Madrid E strain, while OmpB of this latter one and of its virulent variant EVir coincide in mobility. The infectivity of these strains for macrophages was previously shown to be different as well, and to correlate with their virulence. Previously cloned R. prowazekii Breinl strain, 1.644-bp insert from lambda gtll recombinant expressing as OmpB in inducer-independent fashion was sequenced and used as a query to search for similarity in non-redundant GenBank/EMBL/DDBJ Data Base aided by BLASTX mail server. Extensive homology of inferred 282-aa sequence to peptidyl-propyl cis/trans isomerase C (PPIase C) of E. coli belonging to parvulin family of rotamases (foldases), and related proteins such as Campylobacter jejuni cell binding factor 2 (Cbf2), B. subtilis PrsA, and Lactococcus lactis PrtM has been revealed.