Extension of the Minimal Functional Unit of the RNA Polymerase II CTD from yeast to mammalian cells

The carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) consists of 26 and 52 heptad-repeats in yeast and mammals, respectively. Studies in yeast showed that the strong periodicity of the YSPTSPS heptads is dispensable for cell growth and that di-heptads interspersed by spacers can act as minimal functional units (MFUs) to fulfill all essential CTD functions. Here, we show that the MFU of mammals is significantly larger than in yeast and consists of penta-heptads. We further show that the distance between two MFUs is critical for the functions of mammalian CTD. Our study suggests that the general structure of the CTD remained largely unchanged in yeast and mammals, however, besides the number of heptad-repeats, also the length of the MFU significantly increased in mammals.RNA聚合酶II（Pol II）最大亚基的羧基末端结构域（CTD）在酵母和哺乳动物中分别包含26个和52个七肽重复序列。过往针对酵母的研究显示，YSPTSPS七肽的强周期性对细胞生长并非不可或缺，且由间隔序列隔开的双联七肽可充当最小功能单元（MFUs），以执行CTD的全部核心功能。本研究证实，哺乳动物的最小功能单元（MFU）显著大于酵母，且由五联七肽构成；我们进一步发现，两个最小功能单元之间的间距对哺乳动物CTD的功能具有关键影响。本研究表明，尽管CTD的整体结构在酵母与哺乳动物中大体保持保守，但除七肽重复序列的数量外，哺乳动物的最小功能单元长度也出现了显著增加。