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Mol. Cell. Biol., Feb 1996, 557-563, Vol 16, No. 2
WM Hempel, AH Cavanaugh, RD Hannan, L Taylor and LI Rothblum
Transcription of the 45S rRNA genes is carried out by RNA polymerase I and
at least two trans-acting factors, upstream binding factor (UBF) and SL-1.
We have examined the hypothesis that SL-1 and UBF interact.
Coimmunoprecipitation studies using an antibody to UBF demonstrated that
TATA-binding protein, a subunit of SL-1, associates with UBF in the absence
of DNA. Inclusion of the detergents sodium dodecyl sulfate and deoxycholate
disrupted this interaction. In addition, partially purified UBF from rat
cell nuclear extracts and partially purified SL-1 from human cells
coimmunoprecipitated with the anti-UBF antibody after mixing, indicating
that the UBF-SL-1 complex can re-form. Treatment of UBF-depleted extracts
with the anti-UBF antibody depleted the extracts of SL-1 activity only if
UBF was added to the extract prior to the immunodepletion reaction.
Furthermore, SL-1 activity could be recovered in the immunoprecipitate.
Interestingly, these immunoprecipitates did not contain RNA polymerase I,
as a monospecific antibody to the 194-kDa subunit of RNA polymerase I
failed to detect that subunit in the immunoprecipitates. Treatment of N1S1
cell extracts with the anti-UBF antibody depleted the extracts of SL-1
activity but not TFIIIB activity, suggesting that the binding of UBF to
SL-1 is specific and not solely mediated by an interaction between UBF and
TATA-binding protein, which is also a component of TFIIIB. These data
provide evidence that UBF and SL-1 interact.
Copyright © 1996, American Society for Microbiology
The species-specific RNA polymerase I transcription factor SL-1 binds to upstream binding factor
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822, USA.
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