SEQUENCE CONSERVATION OF THE RAD21 SCHIZOSACCHAROMYCES-POMBE DNA DOUBLE-STRAND BREAK REPAIR GENE IN HUMAN AND MOUSE

The rad21 gene of Schizosaccharomyces pombe is involved in the repair of ionizing radiation-induced DNA double-strand breaks. The isolation of mouse and human putative homologs of rad21 is reported here. Alignm ent of the predicted amino acid sequence of Rad21 with the mammalian p roteins showed that the similarity was distributed across the length o f the proteins, with more highly conserved regions at both termini, Th e mHR21(sp) (mouse homolog of Rad21, S. pombe) and hHR21(sp) (human ho molog of Rad21, S. pombe) predicted proteins were 96% identical, where as the human and S. pombe proteins were 25% identical and 47% similar. RNA blot analysis showed that mHR21(sp) mRNA was abundant in all adul t mouse tissues examined, with highest expression in testis and thymus . In addition to a 3.1-kb constitutive mRNA transcript, a 2.2-kb trans cript was present at a high level in postmeiotic spermatids, while exp ression of the 3.1-kb mRNA in testis was confined to the meiotic compa rtment. hHR21(sp) mRNA was cell cycle regulated in human cells, increa sing in late S phase to a peak in G2 phase. The level of hHR21(sp) tra nscripts was not altered by exposure of normal diploid fibroblasts to 10 Gy ionizing radiation, lit situ hybridization showed that mHR21(sp) resided on chromosome 15D3, whereas hHR21(sp) localized to the synten ic 8q24 region, Elevated expression of mHR21(sp) in testis and thymus supports a possible role for the rad21 mammalian homologs in V(D)J and meiotic recombination, respectively. Cell cycle regulation of rad21, retained from S. pombe to human, is consistent with a conservation of function between S. pombe and human rad21 genes. (C) 1996 Academic Pre ss, Inc.