Na. Hawkes et Sge. Roberts, The role of human TFIIB in transcription start site selection in vitro andin vivo, J BIOL CHEM, 274(20), 1999, pp. 14337-14343
The general transcription factor TFIIB plays a crucial role in selecting th
e transcription initiation site in yeast. We have analyzed the human homolo
gs of TFIIB mutants that have previously been shown to affect transcription
start site selection in the yeast Saccharomyces cerevisiae. Despite the di
stinct mechanisms of transcription start site selection observed in S. cere
visiae and humans, the role of TFIIB in this process is similar. However, u
nlike their yeast counterparts, the human mutants do not show a severe defe
ct in supporting either basal transcription or transcription stimulated by
an acidic activator in vitro. Transient transfection analysis revealed that
, in addition to a role in transcription start site selection, human TFIIB
residue Arg-66 performs a critical function in vivo that is bypassed in vit
ro. Furthermore, although correct transcription start site selection is dep
endent upon an arginine residue at position 66 in human TFIIB, innate funct
ion in vivo is determined by the charge of the residue alone. Our observati
ons raise questions as to the evolutionary conservation of TFIIB and uncove
r an additional function for TFIIB that is required in vivo but can be bypa
ssed in vitro.