DIFFERENTIAL EXPRESSION OF THE RHP51(-POMBE() GENE, A RECA AND RAD51 HOMOLOG FROM THE FISSION YEAST SCHIZOSACCHAROMYCES)

The rhp51(+) gene encodes three transcripts of 1.9, 1.6 and 1.3 kb whi ch have at least six polyadenylation sites, Primer-extension analysis revealed that two transcription start points (tsp) at -166 and -136 we re responsible for the DNA damage inducibility of this gene. Northern blot analyses showed that the three transcripts were expressed differe ntially in response to a variety of DNA damage. During the mitotic cel l cycle, only the largest transcript exhibited periodic expression, re aching the maximal level in front of the cdc22(+) transcript which pea ks at the G1/S boundary. Unexpectedly, the steady-state levels of the three transcripts were differentially regulated during the growth cycl e. The largest and smallest transcripts accumulated in large quantity at the diauxic shift and during the entry into stationary phase, respe ctively. To localize the regions responsible for the differential expr ession of rhp51(+), we constructed rhp51::ura4 and ura4::rhp51 hybrid genes, and analyzed their expression patterns in response to methyl me thanesulfonate (MMS)induced DNA damage. The results showed that the pr omoter region and 5' half of rhp51(+) are sufficient to confer damage- responsiveness while the 3' end of the gene alone can direct the forma tion of multiple, discrete 3' ends of the transcripts. From these resu lts, we conclude that this novel one gene-multiple product system is p ossible through the cooperation of both the promoter and 3' terminal r egions.