Michaelis C, Weeks G
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Biochim Biophys Acta. 1993 Nov 7;1179(2):117-24. doi: 10.1016/0167-4889(93)90132-9.
It has been suggested that cell-type determination in Dictyostelium discoideum is dependent on the position of a cell in the cell cycle at the time of starvation. In order to understand the molecular basis of this phenomenon, we initiated studies on the cell cycle and have recently described the isolation of a Dictyostelium gene encoding a homolog of the Cdc2 kinase. We have been unable to isolate additional cdc2 genes from Dictyostelium using polymerase chain reaction technology, but have isolated a gene that is highly related to cdc2. The encoded product is a protein of 33 kDa that shares over 60% identity to the cell-cycle-dependent Cdc2 kinases. However, despite this high level of identity, the gene is not capable of complementing the temperature-sensitive cdc28 mutant of Saccharomyces cerevisiae. Furthermore, the gene product shares some characteristics with the recently described PCTAIRE proteins; it contains a PCTAIRE motif instead of the Cdc2 kinase conserved PSTAIRE sequence, it does not possess the conserved GDSEID sequence that is involved in the activation of the enzyme and it has a Ser in the position equivalent to Thr-161. However, the Dictyostelium protein exhibits a slightly higher level of identity to the Cdc2 kinases than to the PCTAIRE proteins and is smaller than any of the PCTAIRE proteins thus far identified. Since the gene product has characteristics of both Cdc2 kinases and PCTAIRE proteins we have designated the gene product Crp (Cdc2-Related PCTAIRE) kinase. The gene is expressed as two transcripts of 1.5 and 1.8 kb and the expression is developmentally regulated with low levels of mRNA in vegetative cells and significantly higher levels throughout the remainder of the differentiation process. These results suggest the possibility that the gene product is involved in Dictyostelium differentiation rather than growth. This report is the first evidence for a highly-related cdc2 gene in unicellular eukaryote. It also demonstrates for the first time that a unicellular eukaryote expresses a protein containing the PCTAIRE sequence.
有人提出，盘基网柄菌中的细胞类型决定取决于饥饿时细胞在细胞周期中的位置。为了理解这一现象的分子基础，我们启动了关于细胞周期的研究，并且最近描述了从盘基网柄菌中分离出一个编码Cdc2激酶同源物的基因。我们无法使用聚合酶链反应技术从盘基网柄菌中分离出其他cdc2基因，但分离出了一个与cdc2高度相关的基因。编码产物是一种33 kDa的蛋白质，与细胞周期依赖性Cdc2激酶有超过60%的同一性。然而，尽管有如此高的同一性，该基因却无法互补酿酒酵母的温度敏感型cdc28突变体。此外，该基因产物与最近描述的PCTAIRE蛋白有一些共同特征；它含有一个PCTAIRE基序而非Cdc2激酶保守的PSTAIRE序列，它不具备参与酶激活的保守GDSEID序列，并且在相当于Thr - 161的位置有一个Ser。然而，盘基网柄菌蛋白与Cdc2激酶的同一性水平略高于与PCTAIRE蛋白的同一性水平，并且比迄今为止鉴定出的任何PCTAIRE蛋白都小。由于该基因产物具有Cdc2激酶和PCTAIRE蛋白的特征，我们将该基因产物命名为Crp（Cdc2相关PCTAIRE）激酶。该基因表达为1.5 kb和1.8 kb的两种转录本，其表达受发育调控，营养细胞中mRNA水平较低，而在整个分化过程的其余阶段水平显著更高。这些结果表明该基因产物可能参与盘基网柄菌的分化而非生长。本报告首次证明了单细胞真核生物中存在高度相关的cdc2基因。它还首次证明了单细胞真核生物表达一种含有PCTAIRE序列的蛋白质。
