Data for: A structure-based mechanism for displacement of the HEXIM adapter from 7SK small nuclear RNA

Productive transcriptional elongation of many cellular and viral mRNAs
requires transcriptional factors to extract pTEFb from the 7SK snRNP by
modulating the association between the HEXIM protein and the 7SK snRNA.
 Here we report the structure of the HEXIM arginine-rich motif in
complex with the apical stemloop-1 of 7SK (7SK-SL1apical) and detail how
the HIV transcriptional regulator Tat from various subtypes overcome the
structural constraints required to displace HEXIM. While most interactions
between 7SK and HEXIM and Tat are similar, critical differences exist that
guide function. First, the conformational plasticity of 7SK enables the
formation of three different base pair configurations at a critical
remodeling site, which allows for the modulation required for HEXIM
binding and its subsequent displacement by Tat. Furthermore, the specific
sequence variations observed in various Tat subtypes all converge on
remodeling 7SK at this region. Second, we show that HEXIM primes its own
displacement by causing specific local destabilization upon binding — a
feature that is then exploited by Tat to bind 7SK more efficiently.
Overall, our study details the molecular environment presented by HEXIM
and uncovers a destabilization-driven displacement strategy that increases
the conformational sampling of 7SK-snRNP, which may allow diverse
transcriptional factors to competitively regulate pTEFb.