Amatruda J F, Gattermeir D J, Karpova T S, Cooper J A
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Cell Biol. 1992 Dec;119(5):1151-62. doi: 10.1083/jcb.119.5.1151.
CAP1, the gene encoding the alpha subunit of Saccharomyces cerevisiae capping protein, was cloned using a probe prepared by PCR with primers based on the amino acid sequence of purified alpha subunit peptides. The sequence is similar to that of capping protein alpha subunits of other species but not to that of the S. cerevisiae capping protein beta subunit or any other protein. Null mutants of capping protein, prepared by deletion of the coding region of CAP1 and CAP2 separately or together, are viable and have a similar phenotype. Deletion of the gene for one subunit leads to a loss of protein for the other subunit. The null mutant has a severe deficit of actin cables and an increased number of actin spots in the mother. Cells are round and relatively large. These features are heterogeneous within a population of cells and vary with genetic background. Overexpression of CAP1 and CAP2 also causes loss of actin cables and cell enlargement, as well as the additional traits of aberrant morphogenesis and cell wall thickening. Capping protein null strains and overexpression strains exhibited normal polarized secretion during bud growth as demonstrated by labeling with fluoresceinated Con A. Projection formation and chitin deposition in response to mating pheromone, mating efficiency, and bud site selection were also normal in capping protein null strains. In addition, bulk secretion of invertase was unimpaired. These data indicate that actin cables are not required for polarized secretion in S. cerevisiae.
CAP1是编码酿酒酵母封端蛋白α亚基的基因，使用基于纯化的α亚基肽氨基酸序列设计的引物通过PCR制备的探针进行克隆。该序列与其他物种的封端蛋白α亚基序列相似，但与酿酒酵母封端蛋白β亚基或任何其他蛋白质的序列不同。通过分别或一起缺失CAP1和CAP2的编码区制备的封端蛋白缺失突变体是可行的，并且具有相似的表型。缺失一个亚基的基因会导致另一个亚基的蛋白质缺失。缺失突变体的肌动蛋白电缆严重缺乏，母细胞中的肌动蛋白斑点数量增加。细胞呈圆形且相对较大。这些特征在细胞群体中是异质的，并随遗传背景而变化。CAP1和CAP2的过表达也会导致肌动蛋白电缆的丧失和细胞增大，以及异常形态发生和细胞壁增厚等额外特征。如用荧光素化伴刀豆球蛋白A标记所示，封端蛋白缺失菌株和过表达菌株在芽生长过程中表现出正常的极化分泌。封端蛋白缺失菌株中，响应交配信息素的突起形成和几丁质沉积、交配效率以及芽位选择也正常。此外，蔗糖酶 的大量分泌未受影响。这些数据表明，酿酒酵母中的极化分泌不需要肌动蛋白电缆。
