Disclosed is the discovery that the transcription elongation factor termed
P-TEFb has a central role in transcription elongation control. P-TEFb is herein
shown to phosphorylate RNA polymerase II and to control the transition from abortive
into productive elongation mode. P-TEFb has also been discovered to interact with
the HIV transcriptional transactivating protein, Tat, showing that P-TEFb is the
cellular factor necessary for HIV Tat to effect productive viral mRNA elongation.
The invention provides genes encoding P-TEFb subunits, including human genes, and
related biological components, and also provides assay methods connected with the
control of transcription elongation. Particularly useful assays are those concerning
the identification of substances that inhibit viral replication at the transcription
elongation stage by inhibiting the binding or functional interaction of viral proteins
to P-TEFb.