Seum Carole, Pauli Daniel, Delattre Marion, Jaquet Yannis, Spierer Anne, Spierer Pierre
Department of Zoology and Animal Biology, University of Geneva, 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
Genetics. 2002 Jul;161(3):1125-36. doi: 10.1093/genetics/161.3.1125.
The Su(var)3-7 gene, a haplo-suppressor and triplo-enhancer of position-effect variegation (PEV), encodes a zinc finger heterochromatin-associated protein. To understand the role of this protein in heterochromatin and genomic silencing, mutations were generated by homologous recombination. The donor fragment contained a yellow(+) gene and 7.6 kb of the Su(var)3-7 gene inserted between two FRTs. The Su(var)3-7 sequence contained three stop codons flanking an I-SceI cut site located in the 5' half of the gene. Using two different screening approaches, we obtained an allelic series composed of three mutant alleles. The three mutations are dominant suppressors of PEV. One behaves as a null mutation and results in a maternal-effect recessive lethal phenotype that can be rescued by a zygotic paternal wild-type gene. A P transposon zygotically expressing a Su(var)3-7 full-length cDNA also rescues the mutant phenotype. One hypomorphic allele is viable and the pleiotropic phenotype showed by adult flies indicates that rapidly and late dividing cells seem the most affected by reduced amounts of Su(var)3-7 protein. All three mutants were characterized at the molecular level. Each expresses a portion of the Su(var)3-7 protein that is unable to enter the nucleus and bind chromatin.
Su(var)3 - 7基因是位置效应斑驳（PEV）的单倍体抑制因子和三倍体增强因子，编码一种与异染色质相关的锌指蛋白。为了了解该蛋白在异染色质和基因组沉默中的作用，通过同源重组产生了突变。供体片段包含一个黄色（+）基因和插入两个FRT之间的7.6 kb的Su(var)3 - 7基因。Su(var)3 - 7序列在位于基因5'端一半的I - SceI切割位点两侧包含三个终止密码子。使用两种不同的筛选方法，我们获得了由三个突变等位基因组成的等位基因系列。这三个突变是PEV的显性抑制因子。其中一个表现为无效突变，导致母本效应隐性致死表型，可由合子父本野生型基因挽救。一个合子表达Su(var)3 - 7全长cDNA的P转座子也能挽救突变表型。一个亚效等位基因是可行的，成年果蝇表现出的多效表型表明，快速分裂和晚期分裂的细胞似乎受Su(var)3 - 7蛋白量减少的影响最大。对所有三个突变体进行了分子水平的表征。每个突变体都表达一部分无法进入细胞核并结合染色质的Su(var)3 - 7蛋白。
