Characterization of the function of the NIN1 gene product of Saccharomyces cerevisiae.

The nin1-1 mutant has been isolated as a temperature-sensitive mutant whose nucleus arrested at G2 phase and eventually disintegrated upon temperature upshift. In this study, a genetic event occurring in the nin1-1 mutant was found to be a frameshift mutation, resulting in a truncated protein smaller than the wild-type Nin1 protein. We found new phenotypes associated with the nin1-1 mutation: (i) rates of mitotic recombination and chromosome/plasmid loss in the nin1-1 strain were higher than those in the wild-type strain, and (ii) the mutant was more sensitive to UV irradiation than the wild-type strain. We found dotted structures in the cytoplasm of the wild-type cells by indirect immunofluorescence microscopy using the anti-Nin1 antibody. Similar results were obtained when we analyzed the localization of Nin1-beta-galactosidase fusion protein formed in the cells expressing the NIN-lacZ fusion gene, which is active as NIN1, with anti-beta-galactosidase antibody. The subcellular fractionation method revealed that Nin1 protein was not localized in a particular fraction of the cell lysate.