O. Papoulas et al., The Drosophila trithorax group proteins BRM, ASH1 and ASH2 are subunits ofdistinct protein complexes, DEVELOPMENT, 125(20), 1998, pp. 3955-3966
The trithorax group gene brahma (brm) encodes an activator of Drosophila ho
meotic genes that functions as the ATPase subunit of a large protein comple
x. To determine if BRM physically interacts with other trithorax group prot
eins, we purified the BRM complex from Drosophila embryos and analyzed its
subunit composition. The BRM complex contains at least seven major polypept
ides. Surprisingly, the majority of the subunits of the BRM complex are not
encoded by trithorax group genes. Furthermore, a screen for enhancers of a
dominant-negative brm mutation identified only one trithorax group gene, m
oira (mor), that appears to be essential for brm function in vivo. Four of
the subunits of the BRM complex are related to subunits of the yeast chroma
tin remodeling complexes SWI/SNF and RSC, The BRM complex is even more high
ly related to the human BRG1 and hBRM complexes, but lacks the subunit hete
rogeneity characteristic of these complexes. We present biochemical evidenc
e for the existence of two additional complexes containing trithorax group
proteins: a 2 MDa ASH1 complex and a 500 kDa ASH2 complex. These findings s
uggest that BRM plays a role in chromatin remodeling that is distinct from
the function of most other trithorax group proteins.