Kuang J, Penkala J E, Ashorn C L, Wright D A, Saunders G F, Rao P N
Department of Medical Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Proc Natl Acad Sci U S A. 1991 Dec 15;88(24):11530-4. doi: 10.1073/pnas.88.24.11530.
Maturation-promoting factor (MPF), which is functionally defined by its ability to induce frog oocyte maturation independent of protein synthesis, is hypothesized to be the mitotic inducer in eukaryotic cells. Previous studies have demonstrated that the cdc2 protein kinase complex (p34cdc2-cyclin) meets the criteria for MPF. In the present study, we show that MPF activity in extracts of unfertilized Xenopus eggs can be resolved into three fractions by Q-Sepharose chromatography. Of the total MPF activity recovered, approximately 20% was in the flow-through fraction that was accounted for by the cdc2 kinase complex, approximately 40% was in the 0.2 M NaCl eluate, and the remaining approximately 40% was in the 0.5 M NaCl eluate. Neither eluate contained cdc2 kinase, but each could activate cdc2 kinase upon microinjection into Xenopus oocytes. The MPF activity in the two eluates, but not in the flow-through fraction, could be depleted by the mitosis-specific monoclonal antibody MPM-2. This antibody has been shown to inhibit Xenopus oocyte maturation and deplete MPF activity from mature oocyte extract but does not recognize the cdc2 kinase complex. The three MPFs differed in apparent molecular size, H1 kinase activity, and stability at 4 degrees C. We propose that MPF activity in unfertilized Xenopus eggs resides in at least three different molecular species, the combined activities of which may be required for autoamplification of MPF.
促成熟因子（MPF），其功能定义为能够独立于蛋白质合成诱导蛙卵母细胞成熟，被认为是真核细胞中的有丝分裂诱导剂。先前的研究表明，细胞分裂周期蛋白2（cdc2）蛋白激酶复合物（p34cdc2 - 细胞周期蛋白）符合MPF的标准。在本研究中，我们发现未受精的非洲爪蟾卵提取物中的MPF活性通过Q - 琼脂糖凝胶层析可分为三个组分。回收的总MPF活性中，约20%存在于穿透组分中，由cdc2激酶复合物构成，约40%存在于0.2M NaCl洗脱液中，其余约40%存在于0.5M NaCl洗脱液中。两种洗脱液中均不含cdc2激酶，但将它们显微注射到非洲爪蟾卵母细胞中时均可激活cdc2激酶。两种洗脱液中的MPF活性，而非穿透组分中的MPF活性，可被有丝分裂特异性单克隆抗体MPM - 2耗尽。已证明该抗体可抑制非洲爪蟾卵母细胞成熟并从成熟卵母细胞提取物中耗尽MPF活性，但不识别cdc2激酶复合物。这三种MPF在表观分子大小、组蛋白H1激酶活性以及4℃下的稳定性方面存在差异。我们提出未受精的非洲爪蟾卵中的MPF活性存在于至少三种不同的分子形式中，其联合活性可能是MPF自身扩增所必需的。
