GENETIC AND BIOCHEMICAL-ANALYSIS OF PHOTOLYASE MUTANTS OF CHLAMYDOMONAS-REINHARDTII

A mutant of Chlamydomonas reinhardtii phr-1-1 is deficient in the phot orepair of pyrimidine dimers in nuclear DNA but not in chloroplast DNA . In this report, a second photoreactivation-deficient strain, phr-1-2 , which has a similar phenotype as phr-1-1, is described. To determine if these mutations were in different genes, complementation tests as well as tetrad analysis were performed. Six diploid strains were const ructed. The diploid strains containing one mutation exhibited similar UV-light survival curves under photoreactivating conditions as the wil d-type diploid, indicating recessive nature of the mutations. No incre ase in survival was obtained with phr-1-1 phr-1-2 compared with either the phr-1-1 phr-1-1 or phr-1-2 phr-1-2 diploids indicating a lack of complementation. The amount of DNA photolyase activity in cell-free ex tracts of diploids with one mutation was not significantly different f rom extracts of wild-type diploids indicating a lack of gene dosage. T he amount of DNA photolyase activity in extracts from the phr-1-1 phr- 1-2 was no greater than found in the phr-1-1 phr-1-1 or phr-1-2 phr-1- 2 diploids, confirming a lack of complementation of the mutations. Ana lysis of 106 tetrads from a cross of phr-1-1 arg2 x phr-1-2 arg7 indic ated that phr-1-1 and phr-1-2 were mutations in the same gene.