CLONING AND CHARACTERIZATION OF THE ORI REGION OF PSW1200 OF ERWINIA-STEWARTII - SIMILARITY WITH PLASMID P1

The ori region of an Erwinia stewartii plasmid, pSW1200 (106 kb), has been cloned and sequenced. This region consists of a gene encoding a p rotein which has 91% similarity and 73% identity with the RepA protein of bacteriophage P1. The ori region also consists of eight copies of 19-bp iterons which are highly homologous to the iterons of P1. Simila r to plasmid P1, pSW1200 replicon has a copy number of approximately 1 . On the other hand, the copy number increases about ninefold if three of the iterons located downstream from repA gene are deleted. We also demonstrate that pGEM-5Z consisting of a copy of P1 iteron is incompa tible with a pSW1200 derivative, pSW1201, suggesting that pSW1200 and P1 DNA are incompatible and both belong to the IncY group. (C) 1997 Ac ademic Press.