The upr-1 gene encodes a catalytic subunit of the DNA polymerase zeta which is involved in damage-induced mutagenesis in Neurospora crassa.
The upr-1 mutant was one of the first mutagen-sensitive mutants to be isolated in Neurospora crassa. However, the function of the upr-1 gene has not yet been elucidated, although some genetic and biochemical data have been accumulated. In order to clone the upr-1 gene, we performed a chromosome walk from the mat locus, the closest genetic marker to upr-1 for which a molecular probe was available, towards the centromere, and a chromosomal contig of about 300-400 kb was constructed. Some of these clones complemented the temperature sensitivity of the un-16 mutation, which is located between mat and upr-1. The un-16 gene was sequenced, and localized in the MIPS Neurospora crassa genome database. We then searched the regions flanking un-16 for homologs of known DNA repair genes, and found a gene homologous to the REV3 gene of budding yeast. The phenotype of the upr-1 mutant is similar to that of the yeast rev3 mutant. An ncrev3 mutant carrying mutations in the N. crassa REV3 homolog was constructed using the RIP (repeat-induced point mutation) process. The spectrum of mutagen sensitivity of the ncrev3 mutant was similar to that of the upr-1 mutant. Complementation tests between the upr-1 and ncrev3 mutations indicated that the upr-1 gene is in fact identical to the ncrev3 gene. To clarify the role of the upr-1 gene in DNA repair, the frequency of MMS and 4NQO-induced mutations was assayed using the ad-8 reversion test. The upr-1 mutant was about 10 times less sensitive to both chemicals than the wild type. The expression level of the upr-1 gene is increased on exposure to UV irradiation in the uvs-2 and mus-8 mutants, which belong to postreplication repair group, as well as in the wild type. All these results suggest that the product of the upr-1 gene functions in damage-induced mutagenesis and DNA translesion synthesis in N. crassa.
Sakai
W
W
Laboratory of Genetics, Department of Regulation Biology, Faculty of Science, Saitama University, Saitama City 338-8570, Japan.
Ishii
C
C
Inoue
H
H
D020134:Catalytic Domain / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; C425929:DNA polymerase zeta; D004259:DNA-Directed DNA Polymerase; C092602:REV3 protein, S cerevisiae