BUB1 and ataxia telangiectasia: Most importantly, some of the most central and most highly conserved of those genes have human orthologs, mutant alleles of which were found in tumor specimens – among them, SGS1 (human genes BLM and WRN, repair helicase), MRE11 (MRE11A, the gene of a syndrome related to ataxia telangiectasia), DUN1 (CHK2, one of the genes of familial Li–Fraumeni syndrome, coding for a cell cycle checkpoint protein), and BUB1 (BUB1, frequently mutated in colorectal cancer).