Characterization of pSS50 : the 4-Cholorobiphenyl mineralization plasmid

The pSS50 plasmid is a 53.2 Kb self-transmissible plasmid of broad-host range. It was originally isolated from several Alcaligenes and Acinetobacter strains. The distribution of restriction endonuclease cleavage sites on pSS50 is unusual in that there are fewer hexanucleotide recognizing restriction cleavage sites than would be expected based on plasmids of similar size. This paucity of cleavage sites is not due to extensive repetitive sequences. Extensive methylation seems to also not account for the deficit. Of the sites which do occur, the majority are clustered in a 5 Kb region which shows DNA:DNA homology between the right and left sides of that region.

The pSS50 plasmid is not of the Inc I,P,Q,W or Col E1 incompatibility groups. The catabolic genes on pSS50 appear to be positively regulated. Genes for heavy metal resistance have not been found on pSS50. The plasmid has been mutagenized with Tn5 and Tn4431.

Based on the results obtained with pSHS1, a 12 Kb subclone of pSS50 which evenly straddles the restriction site rich region of pSS50, pSS50 must contain an oxygenase determinant within this 12 Kb span.