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Cell. 1998 Feb 20;92(4):451-62.

A novel CDK9-associated C-type cyclin interacts directly with HIV-1 Tat and mediates its high-affinity, loop-specific binding to TAR RNA.

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Regulatory Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037-1099, USA.


The HIV-1 Tat protein regulates transcription elongation through binding to the viral TAR RNA stem-loop structure. We have isolated a novel 87 kDa cyclin C-related protein (cyclin T) that interacts specifically with the transactivation domain of Tat. Cyclin T is a partner for CDK9, an RNAPII transcription elongation factor. Remarkably, the interaction of Tat with cyclin T strongly enhances the affinity and specificity of the Tat:TAR RNA interaction, and confers a requirement for sequences in the loop of TAR that are not recognized by Tat alone. Moreover, overexpression of human cyclin T rescues Tat activity in nonpermissive rodent cells. We propose that Tat directs cyclin T-CDK9 to RNAPII through cooperative binding to TAR RNA.

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