Mutant Male Specific Lethal (MSL) proteins retain MSL3 and MOF ('males absent on first') binding in vitro.FLAG-tagged MSL1 protein (residues 751-1,039) and either full-length haemagglutinin (HA)-MOF, HA-MSL3, or both were coexpressed in Drosophila S2 cells, bound to beads coated with anti-FLAG antibodies, and pelleted. The recovered proteins were visualised with anti-HA antibodies. MSL1 inputs: lane 1, no FLAG plasmid; 2, empty FLAG vector; 3, unrelated FLAG protein of 70 kDa (low molecular weight (LMW)); 4-6, wild-type MSL1; 7, P864L; 8, S943F; 9 F979Z; 10, K1009X; 11, AFG; 12, L940X truncation similar to fragment E in . Bottom: the membrane was stripped and reprobed with antibodies recognising FLAG to visualise the MSL1 proteins. The different sizes reflect different truncations. The unrelated FLAG-tagged protein in lane 2 is much larger than the MSL1 fragments, but was repositioned for comparison.