CHARACTERIZATION OF A CHLAMYDOMONAS-REINHARDTII GENE ENCODING A PROTEIN OF THE DNA PHOTOLYASE BLUE-LIGHT PHOTORECEPTOR FAMILY

The organization and nucleotide sequence of a gene from Chlamydomonas reinhardtii encoding a member of the DNA photolyase/blue light photore ceptor protein family is reported. A region of over 7 kb encompassing the gene was sequenced. Northern analysis detected a single 4.2 kb mRN A. The gene consists of eight exons and seven introns, and encodes a p redicted protein of 867 amino acids. The first 500 amino acids exhibit significant homology with previously sequenced DNA photolyases, showi ng the closest relationship to mustard (Sinapis alba) photolyase (43% identity). An even higher identity, 49%, is obtained when the Chlamydo monas gene product is compared to the putative blue-light photorecepto r (HY4) from Arabidopsis thaliana. Both the Chlamydomonas and the Arab idopsis proteins differ from the well characterized DNA photolyases in that they contain a carboxyl terminal extension of 367 and 181 amino acids, respectively. However, there is very little homology between th e carboxyl terminal domains of the two proteins. A previously isolated Chlamydomonas mutant, phr1, which is deficient in DNA photolyase acti vity, especially in the nucleus, was shown by RFLP analysis not to be linked to the gene we have isolated. We propose this gene encodes a ca ndidate Chlamydomonas blue light photoreceptor.