| dc.description.abstract | High levels of RNA polymerase III gene transcription are achieved
by facilitated recycling of the polymerase on transcription factor
IIIB (TFIIIB)-DNA complexes that are stable through multiple rounds
of initiation. TFIIIB-DNA complexes in yeast comprise the TATA-
binding protein (TBP), the TFIIB-related factor TFIIIB70, and TFIIIB90.
The high stability of the TFIIIB-DNA complex is conferred by
TFIIIB90 binding to TFIIIB70-TBP-DNA complexes. This stability is
thought to result from compound bends introduced in the DNA by
TBP and TFIIIB90 and by protein–protein interactions that obstruct
DNA dissociation. Here we present biochemical evidence that the
high stability of TFIIIB-DNA complexes results from kinetic trapping
of the DNA. Thermodynamic analysis shows that the free energies
of formation of TFIIIB70-TBP-DNA (DG° 5 212.10 6 0.12 kcalymol)
and TFIIIB-DNA (DG° 5 211.90 6 0.14 kcalymol) complexes are
equivalent whereas a kinetic analysis shows that the half-lives of
these complexes (46 6 3 min and 95 6 6 min, respectively) differ
significantly. The differential stability of these isoenergetic com-
plexes demonstrates that TFIIIB90 binding energy is used to drive
conformational changes and increase the barrier to complex
dissociation. | en_US |
