New genes involved in Yersinia pestis fraction I biosynthesis

Antigenic and immunochemical properties of Yersinia pestis fraction I (FI) preparations extracted by different methods were studied with polyclonal and monoclonal antibodies. The existence of mature FI in a form of a complex antigen whose subunits have different genetic control was demonstrated. Galactolipid was shown, with caf1 product, to be the second species-specific component of the FI complex molecule and is probably encoded by chromosomal genes. It, like caf1 product, was expressed in higher quantities at 37°C than at 28°C. Among FI subunits there were at least two proteins of 28 ± 2 kDa and 43 ± 2 kDa which were not specific for Y. pestis but were found also in all Yersinia spp. and some other bacteria. These proteins were synthesised independently of the incubation temperature (4°–40°C) and are possibly encoded chromosomally but outside the caf operon and galactolipid-encoding genes. Both proteins together with galactolipid comprise an envelope antigen found in pFra− or plasmidless Y. pestis strains. Organisation of Y. pestis FI (mature capsular antigen) in the form of a complex of the envelope antigen and the caf1 product is discussed.