Perkins David D, Freitag Michael, Pollard Virginia C, Bailey-Shrode Lori A, Selker Eric U, Ebbole Daniel J
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
Genetics. 2007 Feb;175(2):527-44. doi: 10.1534/genetics.106.065714.
New mutations are found among approximately 20% of progeny when one or both parents carry eas allele UCLA191 (eas(UCLA), easily wettable, hydrophobin-deficient, linkage group II). The mutations inactivate the wild-type allele of cya-8 (cytochrome aa3 deficient, linkage group VII), resulting in thin, "transparent" mycelial growth. Other eas alleles fail to produce cya-8 mutant progeny. The recurrent cya-8 mutations are attributed to repeat-induced point mutation (RIP) resulting from a duplicated copy of cya-8+ that was inserted ectopically at eas when the UCLA191 mutation occurred. As expected for RIP, eas(UCLA)-induced cya-8 mutations occur during nuclear proliferation prior to karyogamy. When only one parent is eas(UCLA), the new mutations arise exclusively in eas(UCLA) nuclei. Mutation of cya-8 is suppressed when a long unlinked duplication is present. Stable cya-8 mutations are effectively eliminated in crosses homozygous for rid, a recessive suppressor of RIP. The eas(UCLA) allele is associated with a long paracentric inversion. A discontinuity is present in eas(UCLA) DNA. The eas promoter is methylated in cya-8 progeny of eas(UCLA), presumably by the spreading of methylation beyond the adjoining RIP-inactivated duplication. These findings support a model in which an ectopic insertion that created a mutation at the target site acts as a locus-specific mutator via RIP.
当一个或两个亲本携带eas等位基因UCLA191（eas（UCLA），易湿润，疏水蛋白缺陷，连锁群II）时，在大约20%的后代中发现了新的突变。这些突变使cya - 8（细胞色素aa3缺陷，连锁群VII）的野生型等位基因失活，导致菌丝体生长细且“透明”。其他eas等位基因未能产生cya - 8突变后代。反复出现的cya - 8突变归因于重复诱导点突变（RIP），这是由于在UCLA191突变发生时，cya - 8 +的一个复制拷贝异位插入到eas位点所致。正如RIP所预期的那样，eas（UCLA）诱导的cya - 8突变发生在核配之前的核增殖过程中。当只有一个亲本是eas（UCLA）时，新的突变仅在eas（UCLA）核中出现。当存在一个长的非连锁重复时，cya - 8的突变受到抑制。在rid（RIP的隐性抑制子）纯合的杂交中，稳定的cya - 8突变被有效消除。eas（UCLA）等位基因与一个长的臂内倒位相关。eas（UCLA）DNA中存在一个不连续区域。在eas（UCLA）的cya - 8后代中，eas启动子被甲基化，推测是由于甲基化从相邻的RIP失活重复区域扩散所致。这些发现支持了一个模型，即一个在靶位点产生突变的异位插入通过RIP作为一个位点特异性诱变剂起作用。
