INSERTIONAL MUTAGENESIS TO ISOLATE ACETATE-REQUIRING MUTANTS IN CHLAMYDOMONAS-REINHARDTII

An arg7 mutant of the green alga Chlamydomonas reinhardtii was transfo rmed with pARG7.8, a plasmid bearing the wild-type ARG7 gene. Out of 4 100 arg+ transformants selected on an arginine-free medium supplemente d with acetate, nine failed to grow on acetate-free medium (ac- mutant s). The results of the genetic and molecular analysis of several ac- m utants are in agreement with the hypothesis that they originated from insertion of the incoming plasmid into the nuclear genome. These mutan ts should constitute valuable tools for isolating the corresponding wi ld-type genes after plasmid rescue into Escherichia coli.