An upstream transcription factor, USF (MLTF), facilitates the formation of preinitiation complexes during in vitro chromatin assembly.

Abstract

During in vitro chromatin assembly the formation of transcription complexes is in direct competition with the assembly of promoter sequences into nucleosomes. Under these conditions the fold stimulation of transcription by an upstream transcription factor (USF) was greater than that observed in the absence of nucleosome assembly. Function of USF during nucleosome assembly required the simultaneous presence of the TATA box binding protein TFIID. Unlike TFIID, USF alone was unable to prevent repression of the promoter during nucleosome assembly. Furthermore, USF displayed reduced or no transcriptional stimulatory activity when added to previously assembled minichromosomes. Under conditions of nucleosome assembly, USF increased the number of assembled minichromosomes which contained stable preinitiation complexes. Subsequent to assembly, the rate at which preformed complexes initiated transcription appeared to be independent of the presence of USF. Thus USF potentiated the subsequent transcriptional activity of the promoter indirectly, apparently by increasing the rate or stability of TFIID binding. This activity resulted in the promoter becoming resistant to nucleosome mediated repression. These observations suggest that some ubiquitous upstream factors, e.g. USF, may play an important role in establishing the transcriptional potential of cellular genes during chromatin assembly.

Isolation of a cDNA for HSF2: evidence for two heat shock factor genes in humans.

“…Transcription reactions were performed as described with "G-less" cassette vectors (20). Nuclear extract from non-heat shocked HeLa cells provided general transcription factors (9 A.l in Fig.…”

H1-mediated Repression of Transcription Factor Binding to a Stably Positioned Nucleosome

“…Lane 1 contains the molecular weight marker. Lanes 2,5,8,11, and 14 are undigested (U) 146-bp core particle DNA. B, location of the histone octamer on the DNA template GUB183-USF45.…”

GAL4 disrupts a repressing nucleosome during activation of GAL1 transcription in vivo.

“…A large body of literature documents changes in chromatin structure in vivo that accompany activation of genes (Eissenberg et al 1985;Gross and Garrard 1987), and accumulating evidence supports important and direct roles for chromatin subunits, that is, nucleosomes, both in preventing expression from repressed genes and in permitting derepression of activated genes (Komberg and Lorch 1991). When promoter sequences are first assembled into chromatin-like structures, their response in vitro to transcriptional activator proteins most closely resembles that observed in vivo {Knezetic and Luse 1986; Workman and Roeder 1987;Knezetic et al 1988;Workman et al 1990Workman et al , 1991Croston et al 1991;Layboum and Kadonaga 1991;Straka and Horz 1991). In this context, nucleosome assembly results in increased fold activation by suppressing basal expression rather than by augmenting induced levels.…”