Human and Rodent Transcription Elongation Factor P-TEFb: Interactions with Human Immunodeficiency Virus Type 1 Tat and Carboxy-Terminal Domain Substrate

AUTOR(ES)

Ramanathan, Y.

FONTE

American Society for Microbiology

RESUMO

The human immunodeficiency virus type 1 transcriptional regulator Tat increases the efficiency of elongation, and complexes containing the cellular kinase CDK9 have been implicated in this process. CDK9 is part of the Tat-associated kinase TAK and of the elongation factor P-TEFb (positive transcription elongation factor-b), which consists minimally of CDK9 and cyclin T. TAK and P-TEFb are both able to phosphorylate the carboxy-terminal domain (CTD) of RNA polymerase II, but their relationships to one another and to the stimulation of elongation by Tat are not well characterized. Here we demonstrate that human cyclin T1 (but not cyclin T2) interacts with the activation domain of Tat and is a component of TAK as well as of P-TEFb. Rodent (mouse and Chinese hamster) cyclin T1 is defective in Tat binding and transactivation, but hamster CDK9 interacts with human cyclin T1 to give active TAK in hybrid cells containing human chromosome 12. Although TAK is phosphorylated on both serine and threonine residues, it specifically phosphorylates serine 5 in the CTD heptamer. TAK is found in the nuclear and cytoplasmic fractions of human cells as a large complex (∼950 kDa). Magnesium or zinc ions are required for the association of Tat with the kinase. We suggest a model in which Tat first interacts with P-TEFb to form the TAK complex that engages with TAR RNA and the elongating transcription complex, resulting in hyperphosphorylation of the CTD on serine 5 residues.

Documentos Relacionados

• Transcription elongation factor P-TEFb is required for HIV-1 Tat transactivation in vitro
• Inhibition of Human Immunodeficiency Virus Type 1 Replication by RNA Interference Directed against Human Transcription Elongation Factor P-TEFb (CDK9/CyclinT1)
• Coordination of Transcription Factor Phosphorylation and Histone Methylation by the P-TEFb Kinase during Human Immunodeficiency Virus Type 1 Transcription
• Specific interaction of Tat with the human but not rodent P-TEFb complex mediates the species-specific Tat activation of HIV-1 transcription
• Efficient Particle Production by Minimal Gag Constructs Which Retain the Carboxy-Terminal Domain of Human Immunodeficiency Virus Type 1 Capsid-p2 and a Late Assembly Domain