TFA interacts with the TBP subunit of TFD and aids in the binding of TBP to TATA-box containing promoter DNA.  Interaction of TFA with TBP facilitates formation of and stabilizes the preinitiation complex.  Interaction of TFA with TBP also results in the exclusion of negative (repressive) factors that might otherwise bind to TBP and interfere with PIC formation. TFA also acts as a coactivator for some transcriptional activators, assisting with their ability to increase, or activate, transcription. The requirement for TFA in vitro transcription systems has been variable, and it can be considered either as a GTF and/or a loosely associated TAF-like coactivator.  Genetic analysis in yeast has shown that TFA is essential for viability.