Rastelli L, Chan C S, Pirrotta V
Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030.
EMBO J. 1993 Apr;12(4):1513-22. doi: 10.1002/j.1460-2075.1993.tb05795.x.
Polycomb group genes are necessary for maintaining homeotic genes repressed in appropriate parts of the body plan. Some of these genes, e.g. Psc, Su(z)2 and E(z), are also modifiers of the zeste-white interaction. The products of Psc and Su(z)2 were immunohistochemically detected at 80-90 sites on polytene chromosomes. The chromosomal binding sites of these two proteins were compared with those of zeste protein and two other Polycomb group proteins, Polycomb and polyhomeotic. The five proteins co-localize at a large number of sites, suggesting that they frequently act together on target genes. In larvae carrying a temperature sensitive mutation in another Polycomb group gene, E(z), the Su(z)2 and Psc products become dissociated from chromatin at non-permissive temperatures from most but not all sites, while the binding of the zeste protein is unaffected. The polytene chromosomes in these mutant larvae acquire a decondensed appearance, frequently losing characteristic constrictions. These results suggest that the binding of at least some Polycomb group proteins requires interactions with other members of the group and, although zeste can bind independently, its repressive effect on white involves the presence of at least some of the Polycomb group proteins.
多梳蛋白家族基因对于维持同源异型基因在身体模式适当部位的抑制状态是必需的。其中一些基因，如Psc、Su(z)2和E(z)，也是zeste - white相互作用的调节因子。通过免疫组织化学方法在多线染色体上80 - 90个位点检测到了Psc和Su(z)2的产物。将这两种蛋白质的染色体结合位点与zeste蛋白以及另外两种多梳蛋白家族蛋白Polycomb和多同源异型蛋白的结合位点进行了比较。这五种蛋白质在大量位点共定位，表明它们经常共同作用于靶基因。在另一个多梳蛋白家族基因E(z)中携带温度敏感突变的幼虫中，在非允许温度下，Su(z)2和Psc产物从大多数但不是所有位点的染色质上解离，而zeste蛋白的结合不受影响。这些突变幼虫中的多线染色体呈现出解聚的外观，经常失去特征性的缢痕。这些结果表明，至少一些多梳蛋白家族蛋白的结合需要与该家族的其他成员相互作用，并且尽管zeste可以独立结合，但其对白色基因的抑制作用涉及至少一些多梳蛋白家族蛋白的存在。
