Regulation of the RAD6 gene of Saccharomyces cerevisiae in the mitotic cell cycle and in meiosis.

The regulation of the RAD6 gene at the mRNA level was investigated. The level of steady state RAD6 mRNA increases once every cell cycle, at late S/early G2. This stage is the one at which rad6 mutants arrest, as do wild-type cells exposed to hydroxyurea (HU) or methyl methanesulfonate (MMS), or cdc40 cells exposed to the restrictive temperature. This appears to be a repair-specific stage in the cell cycle. RAD6 mRNA levels increase when cells are treated with MMS, but this increase seems to be due to the arrest of the cells by MMS at the repair-specific stage; cells arrested at the same stage by HU or by the cdc40 lesion also show high levels of RAD6 mRNA. A much smaller increase in the level of RAD6 transcripts is seen following UV irradiation. During meiosis, RAD6 mRNA is more abundant before commitment to recombination. The differential increase of RAD6 mRNA during the S/G2 repair-specific stage of the cell cycle relates the RAD6 function to the normally occurring radioresistance found at this stage.