Genetic analysis of the low calcium response in Yersinia pestis mu d1(Ap lac) insertion mutants

Abstract

Y. pestis strain KIM requires plasmid pCD1 for expression of the low Ca response, plague virulence antigen V and virulence. Mu d1(Ap lac) insertion mutants of this plasmid which were unable to express the low Ca response were constructed. The insertions mapped to a 17-kilobase region of the plasmid. By determining the orientation of the insertions and examining .beta.-galactosidase production from the Mu d1 lac genes, it was determined that this region contains 3 units of transcription, 1 of which is transcribed in a direction opposite the direction of transcription of the other 2. Transcription of at least 2 of these units was induced significantly at 37.degree. C compared with 26.degree. C. Ca2+ (2.5 mM) and ATP (18 mM) had no significant effect on the level of expression of the Mu d1 lac genes of these mutants. All insertions in the region strongly reduced production of the V antigen. Insertions from each unit of transcription also reduced virulence in mice.