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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Amino Acid Substitution
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Base Sequence
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Genes, fos
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HeLa Cells
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Humans
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In Vitro Techniques
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Models, Biological
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Molecular Sequence Data
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Nuclear Proteins / chemistry*
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Phosphorylation
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Positive Transcriptional Elongation Factor B / genetics
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Positive Transcriptional Elongation Factor B / metabolism*
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Protein Structure, Tertiary
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RNA / genetics
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RNA / metabolism
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RNA Polymerase II / metabolism
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Recombinant Proteins / chemistry
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Repetitive Sequences, Amino Acid
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Threonine / chemistry
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Transcription Factors / chemistry
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription, Genetic
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Transcriptional Elongation Factors / chemistry*
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Transcriptional Elongation Factors / genetics
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Transcriptional Elongation Factors / metabolism*
Substances
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Nuclear Proteins
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Recombinant Proteins
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SUPT5H protein, human
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Transcription Factors
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Transcriptional Elongation Factors
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Threonine
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RNA
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Positive Transcriptional Elongation Factor B
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RNA Polymerase II