Abstract: Our previous work suggests that the Nhp6 HMGB protein stimulates RNA polymerase II transcription via the TATA-binding protein TBP, and that Nhp6 functions in the same functional pathway as the Gcn5 histone acetyltransferase. In this report we examine the genetic relationship between Nhp6 and Gcn5 with the Mot1 and Ccr4-Not complexes, which have both been implicated in regulating DNA-binding by TBP. We find that combining either a nhp6ab or a gcn5 mutation with mot1, ccr4, not4 or not5 mutations results in lethality. Combining TBP point mutations with either mot1 or ccr4 also results in either a growth defect or lethality. Several of these synthetic lethalities can be suppressed by overexpression of TFIIA, TBP, or Nhp6, suggesting these genes facilitate formation of the TBP-TFIIA-DNA complex. The growth defect of a not5 mutant can be suppressed by a mot1 mutant. HO gene expression is reduced by nhp6ab, gcn5, or mot1 mutations, and the additive decreases in HO mRNA levels in nhp6ab mot1 and gcn5 mot1 strains suggest different modes of action. Chromatin immunoprecipitation experiments show decreased binding of TBP to promoters in mot1 mutants, and a further decrease when combined with either nhp6ab or gcn5 mutations.