The RAD6 gene of Saccharomyces cerevisiae encodes a ubiquitin-conjugating (E2) enzyme and is required for the repair of damaged DNA, mutagenesis, and sporulation. Here, we report our studies on the regulation of RAD6 gene expression after UV damage, during the mitotic cell cycle, in meiosis, and following heat shock and starvation. RAD6 mRNA levels became elevated in cells exposed to UV light, and at all UV doses the Increase in mRNA levels was rapid and occurred within 30 min after exposure to UV. RAD6 mRNA levels also increased in sporulating MATa/MATα cells, and the period of maximal accumulation of RAD6 mRNA during melosis is coincident with the time during which recombination occurs. However, RAD6 mRNA levels showed no periodic fluctuation in the mitotic cell cycle, were not elevated upon heat shock, and fell in cells in the stationary phase of growth. These observations suggest that RAD6 activity is required throughout the cell cycle rather than being restricted to a specific stage, and that during melosis, high levels of RAD6 activity may be needed at a stage coincident with genetic recombination. The observation that RAD6 transcription is not Induced by heat and starvation, treatments that activate stress responses, suggests that the primary role of RAD6 is in the repair of damaged DNA rather than in adapting cells to stress situations.
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