CHARACTERIZATION OF THE BASIC REPLICON OF PCM1, A NARROW-HOST-RANGE PLASMID FROM THE MODERATE HALOPHILE CHROMOHALOBACTER-MARISMORTUI

The moderately halophilic bacterium Chromohalobacter marismortui conta ins a 17.5-kb narrow-host-range plasmid, pCM1, which shows interesting properties for the development of cloning vectors for the genetic man ipulation of this important group of extremophiles. Plasmid pCM1 can s tably replicate and is maintained in most gram-negative moderate halop hiles tested. The replication origin has been identified and sequenced , and the minimal pCM1 replicon has been localized to a 1,600-bp regio n which includes two functionally discrete regions, the oriV region an d the repA gene. oriV, located on a 700-bp fragment, contains four ite rons 20 bp in length adjacent to a DnaA box that is dispensable but re quired for efficient replication of pCM1, and it requires trans-acting functions. The repA gene, which encodes a replication protein of 289 residues, is similar to the replication proteins of other gram-negativ e bacteria.