Article

P-TEFb-Mediated Phosphorylation of hSpt5 C-Terminal Repeats Is Critical for Processive Transcription Elongation

Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8501, Japan.
Molecular Cell (Impact Factor: 14.02). 02/2006; 21(2):227-37. DOI: 10.1016/j.molcel.2005.11.024
Source: PubMed

ABSTRACT

Human DSIF, a heterodimer composed of hSpt4 and hSpt5, plays opposing roles in transcription elongation by RNA polymerase II (RNA Pol II). Here, we describe an evolutionarily conserved repetitive heptapeptide motif (consensus = G-S-R/Q-T-P) in the C-terminal region (CTR) of hSpt5, which, like the C-terminal domain (CTD) of RNA Pol II, is highly phosphorylated by P-TEFb. Thr-4 residues of the CTR repeats are functionally important phosphorylation sites. In vitro, Thr-4 phosphorylation is critical for the elongation activation activity of DSIF, but not to its elongation repression activity. In vivo, Thr-4 phosphorylation is critical for epidermal growth factor (EGF)-inducible transcription of c-fos and for efficient progression of RNA Pol II along the gene. We consider this phosphorylation to be a switch that converts DSIF from a repressor to an activator. We propose the "mini-CTD" hypothesis, in which phosphorylated CTR is thought to function in a manner analogous to phosphorylated CTD, serving as an additional code for active elongation complexes.

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    • "The exact molecular mechanism underlying this switch remains to be determined, but, in vitro, Cdk9 phosphorylates both DSIF and NELF (Kim and Sharp 2001; Fujinaga et al. 2004) in addition to the Ser2, Thr4, Ser5, and Ser7 residues of the Pol II CTD (Ramanathan et al. 2001; Glover-Cutter et al. 2009; Hsin et al. 2011). Phosphorylation by Cdk9 of the Spt5 C-terminal repeat (CTR) regions potentiates the elongation stimulatory activity of DSIF in vitro (Yamada et al. 2006). P-TEFb has also been reported to modify transcriptional activators and coactivators (Alarcon et al. 2009; Dobrovolna et al. 2012) and a component of a histone modification pathway (Shchebet et al. 2012). "
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    • "However, NusG functions as a monomer in bacteria as the Spt4 homologue does not exist in this domain of life (Ponting, 2002). NusG and Spt4:Spt5 are widely accepted as elongation factors that stimulate transcription elongation and RNAP processivity (Kwak et al., 2003; Mooney et al., 2009; Yamada et al., 2006; Zhu et al., 2007); however, these proteins have also been reported to suppress transcription elongation under certain conditions (Core and Lis, 2008; Margaritis and Holstege, 2008; Sevostyanova et al., http://dx.doi.org/10.1016/j.jsb.2015.09.023 1047-8477/Ó 2015 Elsevier Inc. All rights reserved. "
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    • "DSIF, which consists of Spt4 and Spt5, promotes pausing in conjunction with NELF and also serves as a factor required for increasing the catalytic rate of transcription elongation by Pol II. P-TEFb is a kinase that phosphorylates the C-terminal domain (CTD) of RPB1, the largest subunit of Pol II, the C-terminal domain of SPT5, and the NELF-E subunit to promote the transition to transcription elongation (Fujinaga et al., 2004; Marshall et al., 1996; Yamada et al., 2006). The RPB1 CTD contains a heptad repeat (consensus Tyr1- Ser2-Pro3-Thr4-Ser5-Pro6-Ser7) that is subject to extensive post-translational modifications, most notably phosphorylation at Ser2 and Ser5 residues (Smith and Shilatifard, 2013). "
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