Fincham J R, Connerton I F, Notarianni E, Harrington K
Department of Genetics, University of Cambridge, UK.
Curr Genet. 1989 May;15(5):327-34. doi: 10.1007/BF00419912.
Premeiotic inactivation of duplicated sequences (the RIP phenomenon of Selker et al.) was studied by tetrad analysis using ectopic copies of am+ (coding for NADP-specific glutamate dehydrogenase) and a missense allele am3, coding for a distinctive form of the enzyme, at the normal locus. In duplication crosses either both gene copies were inactivated or neither. Two inactivated am3 derivatives were shown to have undergone methylation and numerous base-pair changes, reflected in losses and gains of restriction sites, but without sequence rearrangement. Cutting at restriction sites within the disrupted sequences was incomplete but became almost complete following growth in the presence of 5-azacytidine. In a triplication cross in which one parent carried two unlinked ectopic gene copies together with am3 at the normal locus, premeiotic inactivation, when it occurred, tended to affect two of the three copies in any one ascus, but there were a few asci in which all three were inactivated.
通过四分体分析，利用正常位点上am⁺（编码NADP特异性谷氨酸脱氢酶）的异位拷贝和编码该酶独特形式的错义等位基因am3，研究了重复序列的减数分裂前失活（Selker等人的RIP现象）。在重复杂交中，要么两个基因拷贝都失活，要么都不失活。两个失活的am3衍生物显示发生了甲基化和大量碱基对变化，这反映在限制性酶切位点的增减上，但没有序列重排。在 disrupted 序列内的限制性酶切位点处的切割不完全，但在5-氮杂胞苷存在下生长后几乎完全。在一个三重杂交中，一个亲本在正常位点携带两个不连锁的异位基因拷贝以及am3，减数分裂前失活一旦发生，往往会影响任何一个子囊中三个拷贝中的两个，但有少数子囊所有三个拷贝都失活。
