Abstract
The C-terminal domain (CTD) of RNA polymerase II (Pol II) consists of conserved heptapeptide repeats that function as a binding platform for different protein complexes involved in transcription, RNA processing, export, and chromatin remodeling. The CTD repeats are subject to sequential waves of posttranslational modifications during specific stages of the transcription cycle. These patterned modifications have led to the postulation of the “CTD code” hypothesis, where stage-specific patterns define a spatiotemporal code that is recognized by the appropriate interacting partners. Here, we highlight the role of CTD modifications in directing transcription initiation, elongation, and termination. We examine the major readers, writers, and erasers of the CTD code and examine the relevance of describing patterns of posttranslational modifications as a “code.” Finally, we discuss major questions regarding the function of the newly discovered CTD modifications and the fundamental insights into transcription regulation that will necessarily emerge upon addressing those challenges.
Highlights
The transcription of DNA to RNA in eukaryotes is catalyzed by three structurally related RNA polymerases, with each acting on a different class of genes [1]
The most studied polymerase is RNA Polymerase II (Pol II), which is responsible for the transcription of proteincoding genes, small nuclear RNA, and small nucleolar RNA [6,7,8]
Pol II transcribes cryptic unstable transcripts (CUTs) and stable unannotated transcripts (SUTs), which are degraded after synthesis [11,12,13]
Summary
The transcription of DNA to RNA in eukaryotes is catalyzed by three structurally related RNA polymerases, with each acting on a different class of genes [1]. The CTD serves as the primary point of contact for a wide variety of molecular machines involved in RNA biogenesis during the transcription cycle (reviewed in [8, 22,23,24,25,26,27,28,29,30,31,32]) This domain consists of a highly conserved heptapeptide repeat: Y1S2P3T4S5P6S7 [33,34,35,36]. The yeast CTD can span a distance of up to 650 A , over 4 times the diameter of the core polymerase (Figure 1(b)) [24, 34, 35] The ability of this repetitive sequence to interact with a wide range of nuclear factors stems from the dynamic plasticity of its structure and the diversity of binding surfaces generated by the multitude of post-translational
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