Sung M T, Freedlender E F
Biochemistry. 1978 May 16;17(10):1884-90. doi: 10.1021/bi00603a013.
Previous studies have suggested that the phosphorylation and dephosphorylation of histone H5 play an important role in controlling the condensation of avian erythrocyte chromatin. The present work locates in the polypeptide chain the major sites at which H5 is phosphorylated in vivo. The majority of the radioactivity in 32P-labeled H5 is clustered in two regions of the molecule. Nearly 50% of the 32P is found in the amino-terminal N-bromosuccinimide (NBS) peptide (residues 1-28); the remainder is confined to three phosphopeptides arising from the C-terminal half of the molecule (residues 100-200). All phosphopeptides are found in a tryptic digest of monophosphorylated H5, indicating the phosphorylation of a given site is a random event. Automatic Edman degradation of the amino-terminal fragment shows that the radioactivity is equally divided between serines at positions 3 and 7. The C-terminal phosphorylated tryptic peptides share some features with the C-terminal phosphorylation sites in H1. If, as has been postulated, the sites of phosphorylation are in or near DNA combining regions, then H5 may have two DNA combining sites. The location of the phosphorylation sites is discussed in relation to a possible mechanism for controlling chromatin condensation.
先前的研究表明，组蛋白H5的磷酸化和去磷酸化在控制鸟类红细胞染色质的凝聚中起重要作用。目前的工作确定了体内H5发生磷酸化的主要位点在多肽链中的位置。32P标记的H5中的大部分放射性集中在分子的两个区域。在氨基末端的N-溴代琥珀酰亚胺（NBS）肽（第1 - 28位氨基酸残基）中发现了近50%的32P；其余的则局限于由分子C末端一半（第100 - 200位氨基酸残基）产生的三个磷酸肽中。所有磷酸肽都存在于单磷酸化H5的胰蛋白酶消化物中，这表明给定位点的磷酸化是一个随机事件。对氨基末端片段进行自动埃德曼降解表明，放射性在第3位和第7位的丝氨酸之间平均分配。C末端磷酸化的胰蛋白酶肽与H1中的C末端磷酸化位点有一些共同特征。如果如所假设的那样，磷酸化位点位于DNA结合区域内或附近，那么H5可能有两个DNA结合位点。结合控制染色质凝聚的可能机制讨论了磷酸化位点的位置。
