Cloning and Analysis of Neurospora genes which work on homologous recombination

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1) Homologous recombination frequency of several DNA repair mutants were screened by using a plasmid pMTR which carrys Neurospora mtr gene. In the wild type homologous integration of the plasmid into the genome DNA was observed in the frequency of 3 to 5%, but in two strains, mei-3 and mus-25, homologous integrants were not found. Considering other characters of these strains, we speculated that these strains have defects in homologous recombination and recombinational repair.2) We sequenced mei-3 cDNA and genomic DNA.Results showed that the ORF contains three introns and codes a protein of MW38kD.Homology search of this protein showed that MEI3 protein has high homology with Rad51 of Saccharomyces cerevisiae which is similar to recA of Escherichia coli. These proteins are essential for recombination and recombinational repair.3) The mus-25 gene were cloned from Neurospora cosmid library. This gene contained one intron and coded one 93kD protein. Homology search showed that this protein has homology with Rad54 protein of S.cerevisiae. This protein contained 7 domains of helicase and is essential for recombination.