Abstract
The plasmid pSS50 is a 53-kilobase self-transmissible plasmid of broad host range that has been isolated from several Alcaligenes and Acinetobacter species. This plasmid has previously been shown to mediate the mineralization of 4-chlorobiphenyl to carbon dioxide and water. Physical characterization of this plasmid by restriction analysis indicates that most hexanucleotide cleavage sites are clustered in a 5-kilobase region, leaving large regions without restriction sites. The paucity of restriction sites is not due to DNA methylation.