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J. Virol., Aug 1995, 4717-4726, Vol 69, No. 8
MH Kim and DO Peterson
The steroid hormone-inducible promoter of mouse mammary tumor virus (MMTV)
contains three overlapping sequences related to the consensus octamer motif
ATGCAAAT. Basal promoter activity in the absence of hormone induction from
a template in which all three octamer elements were mutated was decreased
by two-to threefold in in vitro transcription assays. Oct-1 protein
purified from HeLa cell nuclear extracts, as well as recombinant Oct-1
expressed in bacteria, recognized MMTV octamer-related sequences, as shown
by DNase I footprinting. Furthermore, rabbit polyclonal antiserum directed
against recombinant Oct-1 completely inhibited the formation of specific
complexes between MMTV octamer-related sequences and proteins present in
nuclear extracts of HeLa cells, indicating that Oct-1 is the major protein
in HeLa nuclear extracts that recognizes octamer-related sequences in the
MMTV promoter. In addition, depletion of Oct-1 from the nuclear extract by
using Oct-1-specific antiserum or a sequence- specific DNA affinity resin
decreased in vitro transcription from the wild-type MMTV promoter to a
level identical to that obtained from a promoter in which all three
octamer-related sequences were mutated. Addition of purified HeLa Oct-1 or
recombinant Oct-1 to the depleted extract selectively increased
transcription from the wild-type relative to the mutated promoter,
demonstrating that Oct-1 transcription factor stimulates basal
transcription from the MMTV promoter. A similar effect was observed when
purified recombinant Oct-2 was added to the Oct-1- depleted extract,
suggesting that Oct-2 may play an important role in MMTV transcription in B
cells.
Copyright © 1995, American Society for Microbiology
Stimulation of basal transcription from the mouse mammary tumor virus promoter by Oct proteins
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128, USA.
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