REGULATION OF M XANTHUS MOTILITY AND DEVELOPMENT

黄色粘球菌是一种形成多细胞的单细胞原核生物 饥饿时含有耐热的分化孢子的结构 以获取营养。我们建议研究MglA，一种必需的GTP结合蛋白 对于这种多细胞结构(果树)的形态发生 体细胞)和孢子的分化，但不利于营养生长。M. 黄花是已知的唯一一种含有黄花蛋白家族蛋白的原核生物。 小分子量(20-25 kDa)的ras样G蛋白。就像它的同源物一样， H-ras，破坏mglA共识GTP结合区的突变 取消其活动。然而，与所有其他真核G蛋白不同的是， 这个家庭，MglA不是必不可少的。 除了影响形态发生和孢子发生外，mglA突变 还取消了机动性。我们的结果表明，MglA与MglB相互作用， 共表达基因在其转录单元中的产物。我们发现了 MglB-LacZ翻译融合会在发育过程中阻止运动，但 在生长过程中不是，这表明MglB-MglA的相互作用是不同的 在生长和发育过程中。本提案中概述的实验包括 旨在从生化角度探索这些相互作用。 MGL的调节机制很复杂。MGL基因突变会影响 至少四个基因在发育过程中的表达，由 Tn5-lac的插入，这可能解释了MGL-突变体未能形成的原因 子实体和孢子。此外，mglA基因还需要 在生长过程中自身表达的激活和自身的抑制 在发育过程中的表达。顺式和反式作用的识别 MGL自动监管所需的要素将提供新的见解 G蛋白信号。 我们发现mglA-突变体的产孢量缺陷可以是 被ras家族中的一种酵母GTP结合蛋白SAR1拯救。因此， MglA突变体不能完全形成耐热孢子 可以用运动缺陷来解释，因为SAR1不能恢复 能动性。需要第二个位点的突变才能恢复运动性缺陷 一株黄曲霉mglA-SAR1菌株。我们建议的突变分析 恢复这种菌株的运动能力将为研究G蛋白提供新的见解 功能。

Myxococcus xanthus is a unicellular prokaryote which forms multicellular structures containing heat-resistant, differentiated spores when starved for nutrients. We propose to study MglA, a GTP-binding protein required for both the morphogenesis of this multicellular structure (a fruiting body) and the differentiation of spores but not for vegetative growth. M. xanthus is the only known prokaryote which has a protein in the family of small (20-25kDa) molecular weight ras-like G-proteins. Like its homolog, H-ras, mutations that destroy the consensus GTP-binding region of mglA abolish its activities. However, unlike all other eukaryotic G-proteins in this family, MglA is not essential. In addition to affecting morphogenesis and sporogenesis, mglA- mutations also abolish motility. Our results show that MglA interacts with MglB, the product of the co-expressed gene in its transcription unit. We have found that mglB-lacZ translational fusions block motility during development but not during growth, suggesting that MglB-MglA interactions are different during growth and development. Experiments outlined in this proposal are aimed at exploring these interactions biochemically. The mechanism of regulation by mgl is complex. mgl- mutations affect expression during development of at least four genes, defined by insertions of Tn5-lac, which may explain why mgl- mutants fail to form fruiting bodies and spores. In addition, the mglA gene is required for activation of its own expression during growth and repression of its own expression during development. Identification of the cis and trans-acting elements required for autoregulation of mgl will provide new insights into G-protein signaling. We have discovered that the sporulation defect of mglA- mutants can be rescued by SAR1, a yeast GTP-binding protein in the ras family. Hence, the inability of mglA- mutants to form heat-resistant spores cannot completely be explained by their motility defect, because SAR1 does not restore motility. It takes a second-site mutation to revert the motility defect of an M. xanthus mglA- SAR1 strain. Our proposed analysis of mutations which restore motility to this strain will provide new insights into G-protein function.