The yeast SWI1, SWI2 (SNF2), and SWI3 genes are required for transcription of HO and INO1 genes. We show that they are also required for transcription of ADH1, ADH2, SUC2, GAL1, and GAL10 and for function of simple UAS elements with binding sites for yeast GAL4 or Drosophila ftz proteins. SWI3 encodes a 99 kd nuclear protein containing a large, highly acidic N-terminal domain. SWI1 is identical to ADR6, which encodes a positive regulator of ADH1 and ADH2. Transcription of HO also requires SNF5 and SNF6. These and other observations suggest that SWI1, SWI2, SWI3, SNF5, and SNF6 may be components of a large multi-subunit complex. We propose that these products perform a general role in transcription by assisting gene-specific regulatory proteins.