COMPLEMENTATION OF THE HHA MUTATION IN ESCHERICHIA-COLI BY THE YMOA GENE FROM YERSINIA-ENTEROCOLITICA - DEPENDENCE ON THE GENE DOSAGE

The Hha protein from Escherichia coli is highly similar (82%) to the Y moA protein from Yersinia enterocolitica. Both are members of a new cl ass of proteins that modulates gene expression. probably by influencin g DNA topology, In this paper, complementation of the hha mutation in E. coli by the ymoA gene from Y. enterocolitica has been studied. We s how that the ymoA gene complements one of the phenotypic properties of hha mutants (high level of haemolysin production when they carry the recombinant plasmid pANN202-312) when cloned in a medium-copy-number p lasmid but not when carried in a low-copy-number plasmid. Western blot analysis of the expression of YmoA in E. coli rules out inefficient e xpression of the protein. Surprisingly, the hha gene itself fails to c omplement the hha mutation when cloned in a medium-copy-number vector and causes genetic rearrangements of the E. coli chromosome as a conse quence of insertion sequences mobilization.