DNA-binding ATPase and transcriptional regulator; forms a high affinity, TATA DNA binding complex with Spt15p (TBP) that has altered specificity, redistributing TBP from TATA-containing to TATA-less promoters; role in displacement of TBP from DNA that involves unbending, followed by ATP-driven, DNA translocation-mediated complex dissociation; coregulates transcription with Spt16p through PIC assembly and nucleosome organization; prevents R-loop accumulation and associated genomic instability