Abstract
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 fulfil all essential CTD functions. Here, we show that the MFU of mammalian cells 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.
Highlights
The carboxy-terminal domain (CTD) of polymerase II (Pol II) is a repetitive low-complexity domain that extends from the large subunit (Rpb1) in eukaryotes
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 fulfil all essential CTD functions
We further show that the distance between two MFUs is critical for the functions of mammalian CTD
Summary
The carboxy-terminal domain (CTD) of Pol II is a repetitive low-complexity domain that extends from the large subunit (Rpb1) in eukaryotes. These CTD variants were viable and showed comparable cell proliferation to that of recombinant wild-type CTD This demonstrates that even within an MFU, mutations at certain positions are tolerated, suggesting that not all residues in MFUs of penta-heptads may be critical for CTD functions in mammalian cells. This is consistent with yeast mutants showing that only the presence of three SP (serine-proline) motifs and two tyrosine residues spaced seven amino acids apart were an absolute requirement for an MFU [14]. Separating MFUs by two AP spacers may affect the recruitment of certain essential transcription factors or affect the CTD-driven aggregation of Pol II [34], altering gene expression
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