ISOLATION OF THE SCHIZOSACCHAROMYCES-POMBE RAD54 HOMOLOG, RHP54(-DAMAGE AND REPLICATION FIDELITY(), A GENE INVOLVED IN THE REPAIR OF RADIATION)

The RAD54 gene of Saccharomyces cerevisiae encodes a putative helicase , which is involved in the recombinational repair of DNA damage, The R AD54 homologue of the fission yeast Schizosaccharomyces pombe, rhp54(), was isolated by using the RAD54 gene as a heterologous probe, The g ene is predicted to encode a protein of 852 amino acids, The overall h omology between the mutual proteins of the two species is 67% with 51% identical amino acids and 16% similar amino acids. A rhp54 deletion m utant is very sensitive to both ionizing radiation and UV, Fluorescenc e microscopy of the rhp54 mutant cells revealed that a large portion o f the cells are elongated and occasionally contain aberrant nuclei. In addition, FAGS analysirs showed an increased DNA content in compariso n with wild-type cells, Through a minichromosome-loss assay it was sho wn that the rhp54 deletion mutant has a very high level of chromosome loss, Furthermore, the rhp54 mutation in either a rad17 or a cdc2.3w m utant background (where the S-phase/mitosis checkpoint is absent) show s a significant reduction in viability, It is hypothesized that the rh p54(+) gene is involved in the recombinational repair of UV and X-ray damage and plays a role in the processing of replication-specific lesi ons.