CLONING OF THE YENI RESTRICTION-ENDONUCLEASE AND METHYLTRANSFERASE FROM YERSINIA-ENTEROCOLITICA SEROTYPE O8 AND CONSTRUCTION OF A TRANSFORMABLE R(-)M(+) MUTANT

Two different clonal groups of pathogenic Yersinia enterocolitica stra ins, American and non-American, have been recognized. These are distin guished by a number of criteria, including their virulence in a murine model of infection. However, genetic analysis of virulence in America n strains has been hampered due to the severe restriction of transform ed or electroporated DNA. Thus, we cloned the yenIMR locus from the Am erican serotype strain 8081c, which encodes YenI, an isoschizomer of P stI. This clone encodes both the restriction endonuclease and methyltr ansferase. The location of the genes on the clone was determined and t his information was used to construct a small deletion (400 bp) that r esults in an R(-)M(+) phenotype. This mutation was recombined onto the Y. enterocolitica chromosome to give an R(-)M(+) M mutant which showe d at least a 1000-fold increase in electroporation frequency compared to the wild-type strain. Southern analysis using a probe derived from yenIMR indicated that American serotype strains have this locus wherea s non-American serotype strains do not.