Distinct cytoplasmic and nuclear fractions of Drosophila heterochromatin protein 1: their phosphorylation levels and associations with origin recognition complex proteins.
Distinct cytoplasmic and nuclear fractions of Drosophila heterochromatin protein 1: their phosphorylation levels and associations with origin recognition complex proteins.
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DOI：
10.1083/jcb.142.2.307
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发表时间：
1998-07-27
期刊：
影响因子：
--
通讯作者：
Kellum R
中科院分区：
文献类型：
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作者：
Huang DW;Fanti L;Pak DT;Botchan MR;Pimpinelli S;Kellum R
异染色质的独特结构特性容纳了多种重要的染色体功能，但我们对其结构仅了解基本的分子细节。分析果蝇结构的一个强大工具是一组突变，这些突变逆转了异染色质对其异位邻近基因表达的抑制作用。已知该组中的几个基因编码富含异染色质的蛋白质。其中最具特征的是异染色质相关蛋白 HP1。 HP1 没有已知的 DNA 结合活性，因此它与异染色质的结合可能依赖于其他蛋白质。为了检查 HP1 相互作用蛋白，我们从早期果蝇胚胎的细胞质中分离出三种不同的 HP1 寡聚体，并分析了它们的组成。这两个较大的寡聚体与与间期细胞核染色质最紧密相关的 HP1 部分具有两个共同特性：磷酸化不足的 HP1 同工型谱以及与起源识别复合物 (ORC) 亚基的关联。我们还发现，ORC2 亚基突变体中 HP1 异染色质定位被破坏。这些发现支持了含有 ORC 的寡聚物在将 HP1 定位到果蝇异染色质中的作用，这与 ORC 在将 Sir1 蛋白招募到酿酒酵母中沉默成核位点中的作用惊人地相似。
The distinct structural properties of heterochromatin accommodate a diverse group of vital chromosome functions, yet we have only rudimentary molecular details of its structure. A powerful tool in the analyses of its structure in Drosophila has been a group of mutations that reverse the repressive effect of heterochromatin on the expression of a gene placed next to it ectopically. Several genes from this group are known to encode proteins enriched in heterochromatin. The best characterized of these is the heterochromatin-associated protein, HP1. HP1 has no known DNA-binding activity, hence its incorporation into heterochromatin is likely to be dependent upon other proteins. To examine HP1 interacting proteins, we isolated three distinct oligomeric species of HP1 from the cytoplasm of early Drosophila embryos and analyzed their compositions. The two larger oligomers share two properties with the fraction of HP1 that is most tightly associated with the chromatin of interphase nuclei: an underphosphorylated HP1 isoform profile and an association with subunits of the origin recognition complex (ORC). We also found that HP1 localization into heterochromatin is disrupted in mutants for the ORC2 subunit. These findings support a role for the ORC-containing oligomers in localizing HP1 into Drosophila heterochromatin that is strikingly similar to the role of ORC in recruiting the Sir1 protein to silencing nucleation sites in Saccharomyces cerevisiae.