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 degrees C than at 28 degrees 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 degrees-40 degrees 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.