Proper RNA processing involves the recruitment of a wide variety of accessory
proteins to the C-terminal domain (CTD) of the largest subunit of RNA
polymerase II (RNAPII), Rpb1 [1]. One regulatory mechanism involves reversible
phosphorylation of the C-terminal domain within RNAPII. The eukaryotic protein
family Rtr1/RPAP2 interacts with the CTD of RNAPII [2]. It has been shown in
yeast that Rtr1 is a CTD phosphatase that regulates RNAPII during the
transition from serine 5 to serine 2 phosphorylation [3]. In addition to Rtr1,
the phosphatases Ssu72 and Fcp1 (see <PDOC50969>) also play an important role
in the regulation of CTD phosphorylation. Rtr1 proteins are poorly conserved
overall, but they share a motif with three strictly conserved Cys residues and
another residue conserved as His (in most fungi) or Cys (in animals and S.
pombe), suggestive of a zinc finger motif (C-x(4)-C-x(n)-C-x(3)-[CH], where n
ranges from 30 to 50) [4,5].
The RTR1-type zinc finger is made of two α helices connected by a long
loop and the three strictly conserved Cys residues are located in this loop
(see <PDB:4FC8>). The fourth ligand of the zinc ion, His or Cys is in the
first turn of the second helix. The zinc ion is coordinated in a tetrahedral
fashion by the four conserved ligands and probably has a structural role,
likely stabilizing the overall structure of the protein [5].
Jeronimo C. Forget D. Bouchard A. Li Q. Chua G. Poitras C. Therien C. Bergeron D. Bourassa S. Greenblatt J. Chabot B. Poirier G.G. Hughes T.R. Blanchette M. Price D.H. Coulombe B.
Title
Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme.
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