Molecular cloning in streptococci: physical mapping of the vehicle plasmid pSM10 and demonstration of intergroup DNA transfer.

The streptococcal resistance plasmid pSM10 (8.3 kb), a deletion derivative of pSM10419 (22.9 kb) determining constitutive erythromycin and lincomycin resistance, was physically mapped with the restriction endonucleases AvaI, AvaII, EcoRI, HpaI, KpnI, PvuII (one site each), HindIII, HaeII (three sites each), HincII (four sites), and HhaI (five sites). Using the cryptic plasmid pVA318 as cloning vehicle, the largest HindIII fragment of pSM10 (3.3 kb) was shown to contain the erythromycin/lincomycin resistance gene(s) of the plasmid. The AvaII site of pSM10 proved to be suitable as a site for cloning AvaII-generated chromosomal DNA fragments from a group C streptococcal strain in the Challis strain of Streptococcus sanguis (group) H). A detailed physical map of the chimeric plasmid pSM10221 (12.8 kb), a fusion product of pSM10 and the staphylococcal chloramphenicol resistance plasmid pC221 (4.5 kb), is also presented. The plasmid chimera has properties making it potentially useful in development of a doubly selective streptococcal cloning vehicle by searching for insertional inactivation.