TN4451 FROM CLOSTRIDIUM-PERFRINGENS IS A MOBILIZABLE TRANSPOSON THAT ENCODES THE FUNCTIONAL MOB PROTEIN, TNPZ

The 6.3 kb Clostridium perfringens transposon Tn4451 encodes a 50 kDa protein, TnpZ, which has amino acid sequence similarity to a group of plasmid mobilization and recombination proteins that comprise the Mob/ Pre family. Members of this family interact with an upstream palindrom ic sequence called an RSA site, and an RSA-like sequence has been iden tified upstream of the tnpZ gene. In Escherichia coil, in the presence of a chromosomally integrated derivative of the broad-host-range IncP plasmid, RP4, TnpZ was able to promote plasmid mobilization in cis an d was able to function in trans to enable the mobilization of a co-res ident plasmid carrying an RSA site. It was also able to mediate the co njugative transfer of plasmids from E. coli to C. perfringens. Site-di rected mutagenesis of two bases within the RSA site resulted in a sign ificant reduction in mobilization frequency, demonstrating that the RS A site is required for efficient plasmid mobilization. TnpZ is the onl y Mob/Pre protein known to be associated with a transposable genetic e lement, and Tn4451 is the first mobilizable but non-self-transmissible transposon to be identified from a Gram-positive bacterium.