ISOLATION AND CHARACTERIZATION OF PLS1 PLASMID MUTANTS WITH INCREASEDCOPY NUMBERS

Streptococcus pneumoniae genetic systems designed for isolation of pla smid mutants with copy-up phenotypes have been developed. The target p lasmids have the pLS1 replicon, and two different strategies have been followed: (i) selection of clones exhibiting augmented resistance to antibiotics, or (ii) obligatory co-existence of incompatible plasmids. We have isolated 23 plasmid mutants exhibiting increased number of co pies. All the mutations corresponded to four different alleles of the copG gene of plasmid pLS 1. These strategies could be used with other plasmids.