Previous Article | Next Article ![]()
Mol. Cell. Biol., 01 1998, 512-524, Vol 18, No. 1
AH Swirnoff, ED Apel, J Svaren, BR Sevetson, DB Zimonjic, NC Popescu and J Milbrandt
Nab proteins constitute an evolutionarily conserved family of corepressors
that specifically interact with and repress transcription mediated by three
members of the NGFI-A (Egr-1, Krox24, zif/268) family of immediate-early
gene transcription factors, which includes NGFI-C, Krox20, and Egr3. We
explored the mechanism of Nab1 repression and identified structural domains
required for Nab1 function. Nab1 does not act by blocking DNA binding or
nuclear localization of NGFI-A. In fact, Nab1 repression is not unique to
NGFI-A because multiple types of non- NGFI-A activation domains were
repressed, as was a heterologous transcription factor carrying the NGFI-A
R1 domain, which is required for Nab1 interaction. Additionally, Nab1
tethered directly to DNA repressed constitutively active promoters.
Tethered repression was not dependent on the identity of the basal promoter
elements, the presence of a distal enhancer, or the distance separating the
binding sites from the promoter. These results suggest that Nab1 repression
is not specific to particular activators and that Nab1 is an active
repressor that works by a direct mechanism. We identified a bipartite-like
nuclear localization sequence and localized the repression function to the
Nab conserved domain 2 (NCD2), a region found in the carboxy- terminal half
of all Nab proteins. Three small regions of homology between Nab1 and
previously characterized corepressors, Dr1 and E1b 55- kDa protein, were
identified within NCD2. Replacement mutagenesis of residues conserved
between these proteins interfered with Nab1 repression, although Nab1 does
not function by the same mechanism as Dr1. The human NAB1 genomic locus was
mapped to chromosome 2q32.3-33.
Copyright © 1998, American Society for Microbiology
Nab1, a corepressor of NGFI-A (Egr-1), contains an active transcriptional repression domain
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
This article has been cited by other articles:
Copyright © 2010 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»