RIBOSOMAL GENES OF YEAST AND THEIR REGULATION

在生长中的酿酒酵母细胞中，核糖体蛋白基因的转录占RNA聚合酶II启动事件的30%。此外，细胞以等摩尔量产生核糖体的80种成分。因此，核糖体的合成不仅需要消耗细胞的大部分资源，还需要进行必要的精细控制，以避免成分之间的不平衡。核糖体的产生不仅受到营养来源和其他外部因素的调节，还受到整合细胞运作的细胞内信号转导通路的调节。从我们的观察中可以明显看出，负责膜合成的分泌途径中的任何缺陷都会导致核糖体RNA和核糖体蛋白基因的合成迅速受到抑制。我们建议沿着两条互锁线研究这一调控的分子基础。(I)我们将努力识别识别137个核糖体蛋白基因中每一个的“签名”，(A)通过突变、嵌合启动子等，(B)通过识别阻遏蛋白激活蛋白Rap1p的活性部位，(C)通过全基因组表达分析来识别任何作为“异常值”的核糖体蛋白基因，即不与其他核糖体蛋白基因协调调控，以及其他可能与核糖体蛋白协调调控的基因集。(Ii)我们将建立一个基因筛查，以确定不再抑制核糖体合成的突变体，以响应分泌途径中的缺陷，希望确定参与者(A)在检测到缺陷时，(B)在通知细胞核的信号转导途径中，以及(C)在对该通知做出反应的转录装置中。由于生长依赖于蛋白质合成，而蛋白质合成依赖于核糖体合成，因此核糖体合成的控制在非常真实的意义上导致了对生长的控制。细胞生长不平衡是许多疾病的原因。我们的希望和期望是，了解核糖体合成调节的基础电路将导致在发生失衡时更有效的干预。

In a growing cell of Saccharomyces cerevisiae transcription of the ribosomal protein genes makes up 30 percent of the RNA polymerase II initiation events. Furthermore, the cell produces the 80 components of the ribosome in equimolar amounts. Thus, the synthesis of ribosomes requires not only the consumption of a major portion of the cell's resources, but also the delicate control necessary to avoid imbalance among the components. The production of ribosomes is regulated not only by the source of nutrients and other external factors, but also by intracellular signal transduction pathways that integrate the operations of the cell. This integration is evident from our observation that any defect in the secretory pathway, responsible for the synthesis of membranes, leads to a rapid repression of the synthesis of both ribosomal RNA and ribosomal protein genes. We propose to investigate the molecular basis of this regulation along two interlocking lines. (I) We will try to identify the 'signature' that identifies each of the 137 ribosomal protein genes, (a) through mutagenesis, chimeric promoters, etc., (b) by identifying the active sites, for this regulation, of the repressor activator protein Rap1p, (c) by using genome-wide expression assays to identify any ribosomal protein gene that is an 'outlier', i.e., is not coordinately regulated coordinately with the others, and for other sets of genes that might be regulated coordinately with the ribosomal proteins. (II) We will set up a genetic screen to identify mutants that no longer repress ribosome synthesis in response to a defect in the secretory pathway, hoping to identify participants (a) in the detection of the defect, (b) in the signal transduction pathway that notifies the nucleus, and (c) in the transcriptional apparatus that responds to that notification. Since growth depends on protein synthesis and protein synthesis depends on ribosome synthesis, the control of ribosome synthesis leads, in a very real sense, to the control of growth. Imbalance in the growth of cells is the cause of much disease. Our hope, and expectation, is that understanding the circuits that underlie the regulation of ribosome synthesis will lead to more effective intervention when an imbalance occurs.