Glycosylation and phosphorylation are mutually exclusive modifications.
Structural images of a heptad repeat in the cis- and trans-conformation are also shown [73–75].
The suppression of CUTs is important to prevent inappropriate transcription within ORFs, to enhance processivity during transcription elongation, and to prevent gene silencing via histone deacetylation [14–18].
Of the twelve Pol II subunits, five are common between the three polymerases [1, 19–21].
The number of times this sequence is repeated varies among eukaryotic organisms, ranging from 15 repeats in amoeba, to 26 repeats in the budding yeast Saccharomyces cerevisiae, to 52 repeats in humans.
An especially unique feature of Pol II is the carboxy-terminal domain (CTD) of its large subunit Rpb1 (Figure 1(a)).
In higher eukaryotes, Pol II generates long noncoding RNA (lnc RNA) and micro RNA (mi RNA) [9, 10].
Pol II also transcribes cryptic unstable transcripts (CUTs) and stable unannotated transcripts (SUTs), which are degraded after synthesis [11–13].
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 .
RNA polymerase I synthesizes most of the ribosomal RNA (r RNA) subunits while RNA polymerase III synthesizes t RNAs, 5S r RNA, and other small RNAs [2–4].