THE MCM2-1 MUTATION OF YEAST CAUSES DNA-DAMAGE WITH A RAD9 REQUIREMENT FOR REPAIR

The minichromosome maintenance mutation, mcm2-1, has been found to synthesize damaged DNA at 35 degrees C. Growth at this temperature rendered the mutant strain more sensitive to killing by ultraviolet irradiation. DNA damage could also be detected by pulsed-field gel electrophoresis, where a higher fraction of the DNA loaded was retained in the inserts at the wells. During the exponential phase of growth at this temperature about 50% of the cells had large buds, with the nucleus at or near the neck of the bud in most cases. The incorporation of the rad9 deletion in the mcm2-1-carrying strain caused a reduction in the percentage of large-budded cells and a moderate loss of cell viability. The results are consistent with mcm2-1 causing DNA damage leading to the arrest of cells in the S/G(2) phase of the cell cycle, which was partially dependent on the RAD9 gene product.