Roseman R R, Swan J M, Geyer P K
Department of Biochemistry, University of Iowa, College of Medicine, Iowa City 52242, USA.
Development. 1995 Nov;121(11):3573-82. doi: 10.1242/dev.121.11.3573.
The suppressor of Hairy-wing [su(Hw)] gene encodes a zinc finger protein that binds to a repeated motif in the gypsy retrotransposon. These DNA sequences, called the su(Hw)-binding region, have properties of an insulator region because they (1) disrupt enhancer/silencer function in a position-dependent manner and (2) protect the mini-white gene from both euchromatic and heterochromatic position effects. To gain further insights into the types of position effects that can be insulated, we determined the effects of the su(Hw)-binding region on dosage compensation of the X-linked mini-white gene. Dosage compensation is the process that equalizes the unequal content of X-linked genes in males and females by increasing the X-linked transcription level twofold in males. Transposition of X-linked genes to the autosomes commonly results in incomplete dosage compensation, indicating that the distinct male X chromatin environment is important for this process. We found that dosage compensation of autosomally integrated mini-white genes flanked by su(Hw)-binding regions was greatly improved, such that complete or nearly complete compensation was observed at the majority of insertion sites. The su(Hw) protein was essential for this enhanced dosage compensation because in a su(Hw) mutant background compensation was incomplete. These experiments provide evidence that the su(Hw)-binding region facilitates dosage compensation of the mini-white gene on the autosomes. This may result from protection of the mini-white gene from a negative autosomal chromatin environment.
毛翅抑制基因[su(Hw)]编码一种锌指蛋白，该蛋白可与逆转座子gypsy中的一个重复基序结合。这些DNA序列被称为su(Hw)结合区域，具有绝缘子区域的特性，因为它们(1)以位置依赖的方式破坏增强子/沉默子功能，(2)保护小白色基因免受常染色质和异染色质位置效应的影响。为了进一步深入了解可以被绝缘的位置效应类型，我们确定了su(Hw)结合区域对X连锁小白色基因剂量补偿的影响。剂量补偿是通过将雄性中X连锁转录水平提高两倍来平衡雄性和雌性中X连锁基因不等含量的过程。X连锁基因易位到常染色体通常会导致不完全的剂量补偿，这表明独特的雄性X染色质环境对这一过程很重要。我们发现，两侧有su(Hw)结合区域的常染色体整合小白色基因的剂量补偿得到了极大改善，以至于在大多数插入位点观察到完全或几乎完全的补偿。su(Hw)蛋白对于这种增强的剂量补偿至关重要，因为在su(Hw)突变背景下补偿是不完全的。这些实验提供了证据，表明su(Hw)结合区域促进了常染色体上小白色基因的剂量补偿。这可能是由于保护小白色基因免受常染色体负染色质环境的影响。
