HOST GROWTH TEMPERATURE AND A CONSERVATIVE AMINO-ACID SUBSTITUTION INTHE REPLICATION PROTEIN OF PPS10 INFLUENCE PLASMID HOST-RANGE

pPS10 is a replicon isolated from Pseudomonas syringae pv. savastanoi that can be established at 37 degrees C efficiently in Pseudomonas aer uginosa but very inefficiently in Escherichia coli. The establishment of the wild-type pPS10 replicon in E. coli is favored at low temperatu res (30 degrees C or below). RepA protein of pPS10 promotes in vitro p lasmid replication in extracts from E. coli, and this replication depe nds on host proteins DnaA, DnaB, DnaG, and SSB. Mutant plasmids able t o efficiently replicate in E. coli at 37 degrees C were obtained. Thre e of four mutants whose mutations were mapped show a conservative Ala- ->Val change in the amino-terminal region of the replication protein R epA. Plasmids carrying this mutation maintain the capacity to replicat e in P. aeruginosa and have a fourfold increase in copy number in this host. The mutation does not substantially alter the autoregulation me diated by RepA. These results show that the physiological conditions o f the host as well as subtle changes in the plasmid replication protei n can modulate the host range of the pPS10 replicon.