Colgan D F, Murthy K G, Prives C, Manley J L
Department of Biological Science, Columbia University, New York 10027, USA.
Nature. 1996 Nov 21;384(6606):282-5. doi: 10.1038/384282a0.
The poly(A) tail found on almost all eukaryotic messenger RNAs is important in enhancing translation initiation and determining mRNA stability. Control of poly(A)-tail synthesis thus has the potential to be a key regulatory step in gene expression and is indeed known to be important during early development in many organisms. To study a possible basis for such regulation, we examined phosphorylation of poly(A) polymerase (PAP) by p34(cdc2)/cyclin B (maturation/mitosis-promoting factor, MPF). We show here that PAP can be phosphorylated in vivo and in vitro by MPF. Consistent with this, PAP becomes hyperphosphorylated both during meiotic maturation of Xenopus laevis oocytes and in HeLa cells arrested at M phase, times in the cell-cycle when MPF is known to be active. We show further that hyperphosphorylation by MPF dramatically reduces the activity of purified PAP, and that PAP isolated from mitotic HeLa cells is similarly inhibited by hyperphosphorylation. This repression probably contributes to the well established reductions in poly(A)+ RNA and/or protein synthesis known to occur in M-phase cells.
几乎所有真核生物信使核糖核酸（mRNA）上的聚腺苷酸（poly(A)）尾在增强翻译起始和决定mRNA稳定性方面都很重要。因此，聚腺苷酸尾合成的调控有可能成为基因表达中的关键调控步骤，并且在许多生物体的早期发育过程中确实已知其很重要。为了研究这种调控的可能基础，我们检测了p34(cdc2)/细胞周期蛋白B（成熟/有丝分裂促进因子，MPF）对聚腺苷酸聚合酶（PAP）的磷酸化作用。我们在此表明，PAP在体内和体外都能被MPF磷酸化。与此一致的是，在非洲爪蟾卵母细胞的减数分裂成熟过程中以及在停滞于M期的HeLa细胞中，PAP都会发生超磷酸化，而这两个时期在细胞周期中MPF已知是有活性的。我们进一步表明，MPF介导的超磷酸化会显著降低纯化后的PAP的活性，并且从有丝分裂期HeLa细胞中分离出的PAP同样会因超磷酸化而受到抑制。这种抑制作用可能导致了M期细胞中已知会出现的聚腺苷酸加尾（poly(A)+）RNA和/或蛋白质合成的显著减少。
