Two genes required for the binding of an essential Saccharomyces cerevisiae kinetochore complex to DNA.

Kinetochores are DNA-protein structures that assemble on centromeric DNA and attach chromosomes to spindle microtubules. Because of their simplicity, the 125-bp centromeres of Saccharomyces cerevisiae are particularly amenable to molecular analysis. Budding yeast centromeres contain three sequence elements of which centromere DNA sequence element III (CDEIII) appears to be particularly important. cis-acting mutations in CDEIII and trans-acting mutations in genes encoding subunits of the CDEIII-binding complex (CBF3) prevent correct chromosome transmission. Using temperature-sensitive mutations in CBF3 subunits, we show a strong correlation between DNA-binding activity measured in vitro and kinetochore activity in vivo. We extend previous findings by Goh and Kilmartin [Goh, P.-Y. & Kilmartin, J.V. (1993) J. Cell Biol. 121, 503-512] to argue that DNA-bound CBF3 may be involved in the operation of a mitotic checkpoint but that functional CBF3 is not required for the assembly of a bipolar spindle. IMAGES:

动粒（kinetochores）是一类组装于着丝粒DNA上、将染色体连接至纺锤体微管的DNA-蛋白质复合物结构。酿酒酵母（Saccharomyces cerevisiae）的125 bp着丝粒因其结构简洁，尤其适合开展分子生物学分析。芽殖酵母的着丝粒包含三类序列元件，其中着丝粒DNA序列元件III（CDEIII）被证实为核心功能元件。CDEIII的顺式作用突变，以及编码CDEIII结合复合物（CBF3）亚基的基因所发生的反式作用突变，均会阻碍染色体的正常传递。本研究借助CBF3亚基的温度敏感型突变体，证实了体外检测得到的DNA结合活性与体内动粒活性之间存在显著相关性。本研究拓展了Goh与Kilmartin的既往研究成果[Goh, P.-Y. & Kilmartin, J.V. (1993) J. Cell Biol. 121, 503-512]，提出DNA结合型CBF3可能参与有丝分裂检验点的调控，但功能性CBF3并非双极纺锤体组装所必需的组分。图像：