Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 277, Issue 16, Pages 13455-13462Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M112038200
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- NCI NIH HHS [CA09673] Funding Source: Medline
- NIAID NIH HHS [AI32489, AI34420] Funding Source: Medline
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The STAT1 transcription factor is organized into several highly conserved domains, each of which has been assigned a function with the exception of the linker domain. We previously characterized a mutant in the linker domain of STAT1 that gave normal DNA binding using a standard probe in an electrophoretic mobility assay but failed to activate transcription in response to interferon gamma. We now report the mechanistic basis for the inactivity of this STAT1(K544A/E545A) mutant. Rather than failing to attract transcriptional coactivators, the STAT1(K544A/E545A) mutant has a subtle biophysical defect, which prevents accumulation of the activated protein on chromatin in vivo: the mutant has comparable K-d with greatly increased k(off) for DNA binding. The increase in both on-rate and off-rate of DNA binding results in a substantially reduced residence time of STAT1(K544A/E545A) on STAT binding sites. We find a similar correlation between off-rate and transcriptional potency for STAT1(N460A), which bears a mutation in the DNA binding domain. These results yield insight into the rate of complex assembly involving STAT1 that leads to transcriptional stimulation.
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