P-TEFb kinase recruitment and function at heat shock loci

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• P-TEFb (a complex of Cdk9 and cyclin T) is known to stimulate transcription elongation in vitro.
• Its precise function and localization in vivo, particularly on chromosomes, remain to be fully elucidated.

Purpose of the Study:

• To investigate the chromosomal localization and function of P-TEFb in Drosophila.
• To determine the role of P-TEFb in transcriptional regulation, especially in response to stress.

Main Methods:

• Immunostaining of Drosophila polytene chromosomes to visualize P-TEFb localization.
• Analysis of P-TEFb recruitment to heat shock loci in wild-type and HSF mutant flies.
• Transcriptional activation assays using a Gal4-P-TEFb hybrid system in Drosophila cells.
• Mutational analysis to assess the importance of Cdk9 kinase activity and cyclin T interaction.

Main Results:

• P-TEFb localizes to over 200 distinct sites on Drosophila polytene chromosomes.
• P-TEFb is rapidly recruited to heat shock loci upon heat shock, dependent on HSF.
• HSF binding alone is insufficient for P-TEFb recruitment, and their localizations are not always coincident.
• Recruitment of a Gal4-P-TEFb hybrid to a promoter activates transcription independently of heat shock.
• P-TEFb-mediated transcriptional stimulation requires Cdk9 kinase activity and interaction with cyclin T.
• P-TEFb frequently colocalizes with hypophosphorylated RNA polymerase II at promoter-pause sites.

Conclusions:

• P-TEFb plays a crucial role in regulating gene expression on Drosophila chromosomes.
• The findings support a model where P-TEFb facilitates the transition of paused RNA polymerase II into productive elongation.
• P-TEFb acts as a key regulator of transcription, particularly in stress response pathways.