Differential expression of the rhp51⁺ gene, a recA and RAD51 homolog from the fission yeast Schizosaccharomyces pombe

The rhp51⁺ f gene encodes three transcripts of 1.9, 1.6 and 1.3 kb which have at least six polyadenylation sites. Primer-extension analysis revealed that two transcription start points (tsp) at -166 and -136 were responsible for the DNA damage inducibility of this gene. Northern blot analyses showed that the three transcripts were expressed differentially in response to a variety of DNA damage. During the mitotic cell cycle, only the largest transcript exhibited periodic expression, reaching the maximal level in front of the cdc22⁺ transcript which peaks at the G1/S boundary. Unexpectedly, the steady-state levels of the three transcripts were differentially regulated during the growth cycle. The largest and smallest transcripts accumulated in large quantity at the diauxic shift and during the entry into stationary phase, respectively, To localize the regions responsible for the differential expression of rhp51⁺, we constructed rhp51::ura4 and ura4::rhp51⁺ hybrid genes, and analyzed their expression patterns in response to methyl methanesulfonate (MMS)-induced DNA damage. The results showed that the promoter region and 5' half of rhp51⁺ are sufficient to confer damage-responsiveness while the 3' end of the gene alone can direct the formation of multiple, discrete 3' ends of the transcripts. From these results, we conclude that this novel one gene-multiple product system is possible through the cooperation of both the promoter and 3' terminal regions.