A cytosine methyltransferase homologue is essential for repeat-induced point mutation in Neurospora crassa
A cytosine methyltransferase homologue is essential for repeat-induced point mutation in Neurospora crassa
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DOI：
10.1073/pnas.132212899
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发表时间：
2002-06-25
影响因子：
11.1
通讯作者：
Selker, EU
中科院分区：
文献类型：
--
作者：
Freitag, M;Williams, RL;Selker, EU
在性发育过程中，粗糙脉孢菌通过重复诱导点突变（RIP）使重复DNA片段中的基因失活。RIP引入C：G到T：A的转换突变，并为随后的营养组织中的DNA甲基化创造目标。RIP的机制及其与DNA甲基化的关系尚未完全了解。DIM-2是一种DNA甲基转移酶（DMT），负责链孢菌中所有已知的胞嘧啶甲基化，DIM-2的突变不能阻止RIP。我们使用RIP来破坏脉孢菌基因组中的第二个假定的DMT基因，并测试DNA甲基化和RIP缺陷的突变体。在可检测的组织中未检测到对DNA甲基化的影响，但突变体在RIP中显示隐性缺陷。在突变的潜在DMT基因纯合的杂交中，am和mtr基因的重复是完全稳定的，我们称之为rid（RIP缺陷型）。在杂合杂交中，相同的重复通常被失活。rid基因的破坏并没有明显影响生育力、生长或发育。相比之下，据报道，对于浸没Ascobolus，masc 1中的相关基因中的突变纯合的杂交不能发育，并且杂合的杂交减少减数分裂前诱导的甲基化[Malagnac，F.，Wendel，B.，Goyon角，Faugeron，G.，Zickler，D.，等人（1997）Cell 91，281-290]。我们从四孢脉孢菌和中间脉孢菌中分离出rid的同源物以鉴定保守区域。同源物具有真核DMT的所有特征基序，并具有大的独特的C-和N-末端结构域。
During sexual development, Neurospora crassa inactivates genes in duplicated DNA segments by a hypermutation process, repeat-induced point mutation (RIP). RIP introduces C:G to T:A transition mutations and creates targets for subsequent DNA methylation in vegetative tissue. The mechanism of RIP and its relationship to DNA methylation are not fully understood. Mutations in DIM-2, a DNA methyltransferase (DMT) responsible for all known cytosine methylation in Neurospora, does not prevent RIP. We used RIP to disrupt a second putative DMT gene in the Neurospora genome and tested mutants for defects in DNA methylation and RIP. No effect on DNA methylation was detected in the tissues that could be assayed, but the mutants showed recessive defects in RIP. Duplications of the am and mtr genes were completely stable in crosses homozygous for the mutated potential DMT gene, which we call rid (RIP defective). The same duplications were inactivated normally in heterozygous crosses. Disruption of the rid gene did not noticeably affect fertility, growth, or development. In contrast, crosses homozygous for a mutation in a related gene in Ascobolus immersus, masc1, reportedly fail to develop and heterozygous crosses reduce methylation induced premeiotically [Malagnac, F., Wendel, B., Goyon, C., Faugeron, G., Zickler, D., et al. (1997) Cell 91, 281-290]. We isolated homologues of rid from Neurospora tetrasperma and Neurospora intermedia to identify conserved regions. Homologues possess all motifs characteristic of eukaryotic DMTs and have large distinctive C- and N-terminal domains.