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起始事件的30%。此外，细胞产生等量的80种核糖体成分。因此，核糖体的合成不仅需要消耗大部分细胞资源，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营养来源和其他外部因素的调节，还受细胞内信号转导途径的调节，这些信号转导途径整合了细胞的运作。这种整合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和核糖体蛋白基因合成的快速抑制。我们建议沿着两条连锁线来研究这种调控的分子基础。(I)我们将尝试识别识别137个核糖体蛋白基因中的每一个的“特征”，(a)通过诱变，嵌合启动子等，(b)通过识别抑制因子激活因子蛋白Rap1p的调节活性位点，(c)通过使用全基因组表达测定来识别任何“异常”的核糖体蛋白基因，即不与其他基因协调调节。对于其他可能与核糖体蛋白协调调节的基因。（II）我们将建立一个基因筛选，以识别不再抑制核糖体合成以响应分泌途径缺陷的突变体，希望识别(a)缺陷检测中的参与者，(b)通知细胞核的信号转导途径中的参与者，以及(c)响应该通知的转录装置中的参与者。由于生长依赖于蛋白质合成，而蛋白质合成又依赖于核糖体合成，因此控制核糖体合成在非常现实的意义上就导致了对生长的控制。细胞生长的不平衡是许多疾病的起因。我们的希望和期望是，了解核糖体合成调控的基础电路，将导致在失衡发生时更有效的干预。

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.