| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2004: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
To understand the cellular-processes involved in genome maintenance, we have developed an assay that analyzes the genetic events responsible for loss of a heterozygous marker (LOH) in yeast diploid cells. This assay allows the quantitative identification of various genetic alterations including chromosome loss, different types of chromosome rearrangements, and point mutations. Our analyses indicate that each of homologous recombination (HR) and post replication repair (PRR) has distinct roles in genome maintenance that cannot be replaced by the other, as well as some interchangeable roles. In other words, the two pathways are operated mostly in a non-mutagenic manner, suggesting the mechanism regulating proper use of the repair pathways in cells. In this respect, SRS2 gene is a postulated regulator in the process via antagonizing HR. To understand the interplay of SRS2, HR and PRR in genome maintenance more precisely, we analyzed LOH events occurring in srs2Δ mutants with the combination of mutations in HR and PRR. Both radI8Δ and srs2Δsingle mutations increased the frequencies of chromosome loss and various chromosome rearrangements and the increase was more prominent in radI8Δ mutants compared to srs2A mutants. Interestingly, in radI8Δ srs2Δ double mutants, the frequencies of chromosome loss and gene conversion were suppressed to the srs2Δ mutant level, whereas interchromosomal crossing over was synergistically increased. These results raise the possibility that SRS2 is directly involved in HR processes and suppresses chromosome loss, in addition to an anti-recombination role. On the other hand, srs2Δ had no effect on LOH events in rad5IΔ background, that is, SRS2 is epistatic to RAD5I for LOH occurrence. In rad52Δ srs2Δ double mutants, however, the frequency of chromosome loss increased synergistically. These results suggest new functions of SRS2 that are required in chromosome maintenance, especially in the absence of RAD52.
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