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Mol Cell Biol, July 1998, p. 3803-3810, Vol. 18, No. 7
Laboratory of Biochemistry and Molecular
Biology, The Rockefeller University, New York, New York 10021-6399
Received 2 February 1998/Returned for modification 20 March
1998/Accepted 22 April 1998
Molecular dissection of the B-cell-specific transcription
coactivator OCA-B has revealed distinct regions important,
respectively, for recruitment to immunoglobulin promoters through
interaction with octamer-bound Oct-1 and for subsequent coactivator
function. Further analysis of general coactivator requirements showed
that selective removal of PC4 from the essential USA fraction severely impairs Oct-1 and OCA-B function in a cell-free system reconstituted with partially purified factors. Full activity can be restored by the
combined action of recombinant PC4 and the PC4-depleted USA fraction,
thus suggesting a joint requirement for PC4 and another, USA-derived
component(s) for optimal function of Oct-1/OCA-B in the reconstituted
system. Indeed, USA-derived PC2 was found to act synergistically with
PC4 in reproducing the function of intact USA in the assay system.
Consistent with the requirement for PC4 in the reconstituted system,
OCA-B was found to interact directly with PC4. Surprisingly, however,
removal of PC4 from the unfractionated nuclear extract has no
detrimental effect on OCA-B/Oct-1-dependent transcription. These
results lead to a general model for the synergistic function of
activation domains in Oct-1 and OCA-B (mediated by the combined action
of the multiple USA components) and, further, suggest a functional
redundancy in general coactivators.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Coactivation by OCA-B: Definition of Critical
Regions and Synergism with General Cofactors

*
Corresponding author. Mailing address: Laboratory of
Biochemistry and Molecular Biology, The Rockefeller University, New
York, NY 10021-6399. Phone: (212) 327-7600. Fax: (212) 327-7949. E-mail: roeder{at}rockvax.rockefeller.edu.
Present address: Laboratory of Molecular Embryology, National
Institute of Child Health and Human Development, National Institutes of
Health, Bethesda, MD 20892-5431.
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