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.