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Mol. Cell. Biol., Feb 1997, 677-686, Vol 17, No. 2
A Basu, B Dong, AR Krainer and CC Howe
The long terminal repeats of murine intracisternal A particles (IAPs)
contain an IAP proximal enhancer (IPE) element that is inactive in murine
F9 embryonal carcinoma cells and active in the parietal endoderm cell line
PYS-2. The element binds efficiently to a 60-kDa IPE-binding protein (IPEB)
present in PYS-2 cells but poorly to F9 proteins, suggesting a role for
IPEB in regulating IAP expression. We have purified calf thymus IPEB, which
binds to the IPE and transactivates a reporter gene in HeLa cell extracts.
Based on the peptide sequence of the purified calf IPEB, we have cloned a
420-bp cDNA and showed that the encoded protein is the homolog of human
p54nrb and mouse NonO, which are characterized by the presence of two RNA
recognition motifs. We show that p54nrb is an IPE-binding transcription
activator with its DNA-binding and activation domains in the N- and
C-terminal halves, respectively. The activation domain of p54nrb is active
in HeLa, PYS-2, and F9 cells, whereas p54nrb as a whole molecule is active
in HeLa and PYS-2 cells but not in F9 cells. Thus, the lack of activity of
p54nrb in F9 cells is due to an ineffective DNA-binding domain. We
demonstrate that p54nrb also binds to a pre-mRNA. Based on the close
sequence relatedness of this protein to PSF, which is required for pre-mRNA
splicing in vitro, we discuss the possibility that p54nrb has dual roles in
transcription and splicing.
Copyright © 1997, American Society for Microbiology
The intracisternal A-particle proximal enhancer-binding protein activates transcription and is identical to the RNA- and DNA-binding protein p54nrb/NonO
The Wistar Institute, Philadelphia, Pennsylvania 19104, USA.
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