The subunits of the yeast SWI/SNF complex were first discovered in genetic screens for their requirement for mating type switching and the use of sucrose as a nutrient source (Neigeborn and Carlson, 1984; Stern et al., 1984). In addition to the ATPase subunit, SWI2/SNF2, the yeast complex includes SWI1/ADR6, SWI3, SNF5 and SNF6 (Cairns et al., 1994), and has an activating role in transcription through chromatin regulation (Table I) (Peterson and Herskowitz, 1992; Hirschhorn et al., 1992; Laurent et al., 1991; Laurent and Carlson, 1992). A homologous complex in Drosophila was also discovered from screens for suppressors of Polycomb mutations that cause homeotic transformations (Tamkun et al., 1992; Elfring et al., 1994). In flies, the core ATPase subunit is a homolog of the yeast SWI2/SNF2, called Brahma (BRM), and the complex is termed the Brahma-associated protein (BAP) complex (Table 1).
