PHH1, A NOVEL GENE FROM ARABIDOPSIS-THALIANA THAT ENCODES A PROTEIN SIMILAR TO PLANT BLUE-LIGHT PHOTORECEPTORS AND MICROBIAL PHOTOLYASES

A cDNA from Arabidopsis thaliana similar to microbial photolyase genes , and designated AT-PHH1, was isolated using a photolyase-like cDNA fr om Sinapsis alba (SA-PHR1) as a probe. Multiple isolations yielded onl y PHH1 cDNAs, and a few blue-light-receptor CRY1 (HY4) cDNAs (also sim ilar to microbial photolyase genes), suggesting the absence of any oth er highly similar Arabidopsis genes. The AT-PHH1 and SA-PHR1 cDNA sequ ences predict 89% identity at the protein level, except for an AT-PHH1 C-terminal extension(lll amino acids), also not seen in microbial pho tolyases. AT-PHH1 and CRY1 show less similarity (54% protein identity) , including respective C-terminal extensions that are themselves mostl y dissimilar. Analysis of fifteen AT-PHH1 genomic isolates reveals a s ingle gene, with three introns in the coding sequence and one in the 5 '-untranslated leader. Full-length AT-PHH1, and both AT-PHH1 and AT-PH H1 Delta C-513 (truncated to be approximately the size of microbial ph otolyase genes) cDNAs, were overexpressed, respectively, in yeast and Escherichia coli mutants hypersensitive to ultraviolet light. The abse nce of significant effects on resistance suggests either that any puta tive AT-PHH1 DNA repair activity requires cofactors/chromophores not p resent in yeast or E. coli, or that AT-PHH1 encodes a blue-light/ultra violet-A receptor rather than a DNA repair protein.