P-TEFb-mediated phosphorylation of hSpt5 C-terminal repeats is critical for processive transcription elongation

Mol Cell. 2006 Jan 20;21(2):227-37. doi: 10.1016/j.molcel.2005.11.024.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Base Sequence
  • Genes, fos
  • HeLa Cells
  • Humans
  • In Vitro Techniques
  • Models, Biological
  • Molecular Sequence Data
  • Nuclear Proteins / chemistry*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Positive Transcriptional Elongation Factor B / genetics
  • Positive Transcriptional Elongation Factor B / metabolism*
  • Protein Structure, Tertiary
  • RNA / genetics
  • RNA / metabolism
  • RNA Polymerase II / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Repetitive Sequences, Amino Acid
  • Threonine / chemistry
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription, Genetic
  • Transcriptional Elongation Factors / chemistry*
  • Transcriptional Elongation Factors / genetics
  • Transcriptional Elongation Factors / metabolism*


  • Nuclear Proteins
  • Recombinant Proteins
  • SUPT5H protein, human
  • Transcription Factors
  • Transcriptional Elongation Factors
  • Threonine
  • RNA
  • Positive Transcriptional Elongation Factor B
  • RNA Polymerase II