Cai S Y, Babbitt R W, Marchesi V T
Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, CT 06536, USA.
Proc Natl Acad Sci U S A. 1999 Mar 16;96(6):2828-33. doi: 10.1073/pnas.96.6.2828.
A new ubiquitin-processing protease (Ubp-M) has been identified in mammalian cells that is phosphorylated at the onset of mitosis and dephosphorylated during the metaphase/anaphase transition. The carboxyl-terminal domain of this 823-aa protein can be phosphorylated in vitro with either extracts of mitotic cells or purified cdc-2/cyclin B complexes. Recombinant Ubp-M is able to deubiquitinate histone H2A in vitro, and the phosphorylated form is also enzymatically active. Wild-type Ubp-M, transiently expressed as green fluorescent protein-fusion proteins, localizes in the cytoplasm of cultured cells, but mutant forms, lacking an active-site cysteine, associate closely with mitotic chromosomes during all stages of cell division and remain within the nucleus during the postmitotic period. Cells transfected with plasmids containing mutant Ubp-M genes stop dividing and eventually undergo apoptosis. Ubp-M may deubiquitinate one or more critical proteins that are involved in the condensation of mitotic chromosomes, possibly acting selectively on histones H2A and H2B, the major ubiquitinated proteins of chromatin.
在哺乳动物细胞中已鉴定出一种新的泛素加工蛋白酶（Ubp-M），它在有丝分裂开始时被磷酸化，并在中期/后期转换期间去磷酸化。这种823个氨基酸的蛋白质的羧基末端结构域在体外能用有丝分裂细胞提取物或纯化的cdc-2/细胞周期蛋白B复合物进行磷酸化。重组Ubp-M在体外能够使组蛋白H2A去泛素化，磷酸化形式也具有酶活性。野生型Ubp-M作为绿色荧光蛋白融合蛋白瞬时表达时，定位于培养细胞的细胞质中，但缺乏活性位点半胱氨酸的突变形式在细胞分裂的所有阶段都与有丝分裂染色体紧密结合，并在有丝分裂后时期保留在细胞核内。用含有突变Ubp-M基因的质粒转染的细胞停止分裂并最终发生凋亡。Ubp-M可能使一种或多种参与有丝分裂染色体凝聚的关键蛋白质去泛素化，可能选择性地作用于组蛋白H2A和H2B，它们是染色质的主要泛素化蛋白质。
