Roseman R R, Pirrotta V, Geyer P K
Department of Biochemistry, University of Iowa, College of Medicine, Iowa City 52242.
EMBO J. 1993 Feb;12(2):435-42. doi: 10.1002/j.1460-2075.1993.tb05675.x.
Mutations in the suppressor of Hairy-wing [su(Hw)] locus reverse the phenotype of a number of tissue-specific mutations caused by insertion of a gypsy retrotransposon. The su(Hw) gene encodes a zinc finger protein which binds to a 430 bp region of gypsy shown to be both necessary and sufficient for its mutagenic effects. su(Hw) protein causes mutations by inactivation of enhancer elements only when a su(Hw) binding region is located between these regulatory sequences and a promoter. To understand the molecular basis of enhancer inactivation, we tested the effects of su(Hw) protein on expression of the mini-white gene. We find that su(Hw) protein stabilizes mini-white gene expression from chromosomal position-effects in euchromatic locations by inactivating negative and positive regulatory elements present in flanking DNA. Furthermore, the su(Hw) protein partially protects transposon insertions from the negative effects of heterochromatin. To explain our current results, we propose that su(Hw) protein alters the organization of chromatin by creating a new boundary in a pre-existing domain of higher order chromatin structure. This separates enhancers and silencers distal to the su(Hw) binding region into an independent unit of gene activity, thereby causing their inactivation.
毛翅抑制因子[su(Hw)]位点的突变可逆转由吉普赛逆转座子插入引起的许多组织特异性突变的表型。su(Hw)基因编码一种锌指蛋白，该蛋白与吉普赛的一个430 bp区域结合，该区域对其诱变作用而言既必要又充分。只有当su(Hw)结合区域位于这些调控序列和启动子之间时，su(Hw)蛋白才会通过增强子元件的失活导致突变。为了理解增强子失活的分子基础，我们测试了su(Hw)蛋白对小白色基因表达的影响。我们发现，su(Hw)蛋白通过使侧翼DNA中存在的负调控元件和正调控元件失活，稳定了常染色质位置上染色体位置效应引起的小白色基因表达。此外，su(Hw)蛋白部分保护转座子插入免受异染色质的负面影响。为了解释我们目前的结果，我们提出su(Hw)蛋白通过在高阶染色质结构的预先存在的结构域中创建一个新的边界来改变染色质的组织。这将su(Hw)结合区域远端的增强子和沉默子分隔成一个独立的基因活性单位，从而导致它们失活。
