Extrachromosomal gene systems in Streptococcus mutans.

1) Four of 86 S. mutans strains of human origin harbor a 3.6 Mdal multicopy plasmid while 2 of 13 strains of rat origin carry multiple copies of a 2.3 Mdal and 2.5 Mdal plasmid. 2) There is no evidence to support that any of these plasmids confers clinically or ecologically important phenotypes. 3) The restriction endonucleases Hind III and Bam HI cleave the 3.6 Mdal plasmid once, thus facilitating the use of this extrachromosomal element in gene cloning systems.