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

• Published in: Molecular cell Vol. 21; no. 2; pp. 227 - 237
• Main Authors: Yamada, Tomoko, Yamaguchi, Yuki, Inukai, Naoto, Okamoto, Sachiko, Mura, Takashi, Handa, Hiroshi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 20.01.2006
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Base Sequence; DNA; 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; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Repetitive Sequences, Amino Acid; RNA - genetics; RNA - metabolism; RNA Polymerase II - metabolism; 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; DNA
• ISSN: 1097-2765; 1097-4164
• 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.