ISOLATION OF CADMIUM SENSITIVE MUTANTS IN CHLAMYDOMONAS-REINHARDTII BY TRANSFORMATION INSERTIONAL MUTAGENESIS/

An arg7, cw15, mt(+) strain of Chlamydomonas reinhardtii (CC1618) was transformed with pARG7.8, a plasmid containing the wild-type ARG7 gene . Over 2300 arg(+) transformants were selected on TAP media. Upon subs equent analysis on TAP plus cadmium plates, five of the transformants failed to grow at a level of 400 mu M cadmium and were designated as c admium sensitive (Cd-s) mutants. Hybridization data indicated that vec tor (pBR329) sequences were present in these five mutants, but not in the untransformed parental strain. Two of the mutants have been back c rossed to an arg7, cw15, Cd+, mt(-) strain (CC425) and found to have p rogeny which always cosegregate the arg(+) and Cd-s phenotypes. This s uggests that the Cd-s phenotype in these two mutants results from the insertion of the plasmid pARG7.8 into a gene involving cadmium detoxif ication, and it provides a method by which to clone the interrupted ge ne(s).