A TRANSPOSON-LIKE SEQUENCE ADJACENT TO THE ACCI RESTRICTION-MODIFICATION OPERON

We have cloned and sequenced the accIRM genes from Weeksella zoohelcum (the original identification of this strain as Acinetobacter calcoace ticus was incorrect). Our sequence differs in the coding regions from a previously published sequence by the addition of three nucleotides n ear the 3' end of the DNA methyltransferase-encoding gene (accIM). We have sequenced approx. 3 kb beyond this operon. Two genes were found, convergently transcribed with the R-M operon. The first of these genes encodes a protein which shows significant similarity to the recombina ses of the phage integrase family. The W. zoohelcum recombinase may fu nction as a transposon resolvase, as in Tn4430. The recombinase-encodi ng gene is followed by a putative transposase (Tnp), which is in turn followed by a terminator which is predicted to be Rho-dependent for th e recombinase-Tnp operon and Rho-independent for the convergent R-M op eron. Since the G+C content of the two operons is notably different, i t is possible that the terminator is at the extremity of the mobile el ement and serves to protect it from incoming transcription.