Mechanisms of cell division with protein phosphorylation.

Hosoya和他的同事发现磷酸化肌球蛋白存在于收缩环中。这对于理解细胞分裂的机制是一个非常重要的发现. Shioda和他的同事们发现了一种新的蛋白质P1，它可以调节DNA复制的起始。P1在其未磷酸化形式下是无活性的，通过磷酸化变得有活性。Ikegami等人从海星卵母细胞中分离到一种新的核酸相关蛋白，命名为NAAP。从NAAP的部分氨基酸序列衍生的寡核苷酸被用来克隆NAAPcDNA，并确定整个cDNA序列。编码NAAP的转录本仅存在于生长的卵母细胞中，而不存在于完全生长的卵母细胞、胚胎和成体组织中。NAAP蛋白定位于成熟卵母细胞的萌发囊泡中，并在成熟卵母细胞减数分裂开始时萌发囊泡破裂后弥散分布。在卵母细胞成熟过程中，NAAP以细胞周期依赖的方式改变分子形态。结果表明，在芽囊泡期未被磷酸化的NAAP的Ser145在减数分裂的M期被磷酸化。

Hosoya and his colleagues discovered that phosphorylated myosin is present in the contractile ring. This is a very importand discovery for the understanding of the mechanism of cell division. They also discovered the enzyme that selectively phosphorylates the light chain of myosin.Shioda and his colleagues discovered a novel protein, P1, which regulates the initiation of DNA replication. P1, which is inactive in its unphosphorylated form, becomes active by phosphorylation. The enzyme responsible for the phosphorylation is found to be a DNA-dependent kinase.Ikegami and his colleagues discovered a novel nucleic-acid associated protein designated as NAAP which was isolated from starfish oocytes. Oligonucleotides derived from the partial amino acid sequences of NAAP were used to clone NAAPcDNA and the entire cDNA sequence was determined. The transcript encoding NAAP was present only in growing oocytes but not in full-grown oocytes, embryos and adult tissues. The NAAP protein localized in the germinal vesicle of the full-grown oocyte and dispersed diffusely after germinal vesicle breakdown at the onset of meiosis. During oocyte maturation, NAAP changed the moleclar form in a cell-cycle dependent manner. It was found that Ser 145 of NAAP,which was unphosphorylated at the germinal vesicle stage, was phosphorylated during the M phase of meiosis.