Bender A, Pringle J R
Department of Biology, University of Michigan, Ann Arbor 48109.
Mol Cell Biol. 1991 Mar;11(3):1295-305. doi: 10.1128/mcb.11.3.1295-1305.1991.
Genes CDC24 and CDC42 are required for the establishment of cell polarity and for bud formation in Saccharomyces cerevisiae. Temperature-sensitive (Ts-) mutations in either of these genes cause arrest as large, unbudded cells in which the nuclear cycle continues. MSB1 was identified previously as a multicopy suppressor of Ts- cdc24 and cdc42 mutations. We have now sequenced MSB1 and constructed a deletion of this gene. The predicted amino acid sequence does not closely resemble any other in the available data bases, and the deletion does not produce any readily detectable phenotype. However, we have used a colony-sectoring assay to identify additional genes that appear to interact with MSB1 and play a role in bud emergence. Starting with a strain deleted for the chromosomal copy of MSB1 but containing MSB1 on a high-copy-number plasmid, mutants were identified in which MSB1 had become essential for viability. The new mutations defined two genes, BEM1 and BEM2; both the bem1 and bem2 mutations are temperature sensitive and are only partially suppressed by MSB1. In bem1 cells, a single copy of MSB1 is necessary and sufficient for viability at 23 or 30 degrees C, but even multiple copies of MSB1 do not fully suppress the growth defect at 37 degrees C. In bem2 cells, a single copy of MSB1 is necessary and sufficient for viability at 23 degrees C, multiple copies are necessary for viability at 30 degrees C, and even multiple copies of MSB1 do not suppress the growth defect at 37 degrees C. In a wild-type background (i.e., a single chromosomal copy of MSB1), both bem1 and bem2 mutations cause cells to become large and multinucleate even during growth at 23 degrees C, suggesting that these genes are involved in bud emergence. This suggestion is supported for BEM1 by other evidence obtained in a parallel study (J. Chant, K. Corrado, J. Pringle, and I. Herskowitz, submitted for publication). BEM1 maps centromere distal to TYR1 on chromosome II, and BEM2 maps between SPT15 and STP2 on chromosome V.
基因CDC24和CDC42对于酿酒酵母细胞极性的建立以及芽的形成是必需的。这两个基因中任何一个的温度敏感（Ts-）突变都会导致细胞停滞成为大型的、未出芽的细胞，而核周期仍在继续。MSB1先前被鉴定为Ts-cdc24和cdc42突变的多拷贝抑制子。我们现在已对MSB1进行了测序并构建了该基因的缺失突变体。预测的氨基酸序列与现有数据库中的任何其他序列都不太相似，并且该缺失并未产生任何易于检测到的表型。然而，我们使用了菌落扇形分析法来鉴定其他似乎与MSB1相互作用并在芽出现过程中起作用的基因。从缺失了染色体上MSB1拷贝但在高拷贝数质粒上含有MSB1的菌株开始，鉴定出了其中MSB1对生存力变得至关重要的突变体。新的突变定义了两个基因，即BEM1和BEM2；bem1和bem2突变都是温度敏感型的，并且仅被MSB1部分抑制。在bem1细胞中，单拷贝的MSB1对于在23或30摄氏度下的生存力是必需且足够的，但即使多个拷贝的MSB1也不能完全抑制37摄氏度时的生长缺陷。在bem2细胞中，单拷贝的MSB1对于在23摄氏度下的生存力是必需且足够的，多个拷贝对于在30摄氏度下的生存力是必需的，并且即使多个拷贝的MSB1也不能抑制37摄氏度时的生长缺陷。在野生型背景下（即单个染色体拷贝的MSB1），bem1和bem2突变都会导致细胞即使在23摄氏度生长期间也变得很大且多核，这表明这些基因参与芽的出现。在一项平行研究中获得的其他证据（J. Chant、K. Corrado、J. Pringle和I. Herskowitz，已提交发表）支持了BEM1的这一推测。BEM1定位于染色体II上TYR1的着丝粒远端，而BEM2定位于染色体V上SPT15和STP2之间。
