Recombinant Knirps protein is present in a large molecular weight complex, cofractionating with CtBP and Rpd3. Crude extracts containing FLAG-tagged Knirps protein was passed over a Superdex 200 gel filtration column, and even numbered fractions were assayed by Western blot. A, Peak Knirps levels were detected in fraction 18 with anti-FLAG antibodies. Inp, input. Asterisk, nonspecific band. Phosphorylated Knirps species in input lane marked by bracket. B, Rpd3 protein was detected in fraction 18, and in smaller molecular weight complexes. C, Larger amounts of fractions around peak fraction 18 were assayed by Western blot, showing presence of Knirps protein in flanking fractions. D, Rpd3 and CtBP proteins were detected in these Knirps-containing fractions. E, Immunoprecipitation of Knirps protein from embryo nuclear extract using anti-FLAG antibody (FL, lane 4) enriches Rpd3 protein over levels obtained by immunoprecipitation using nonspecific IgG (lane 5). Rpd3 protein present in nuclear extract starting material (NE) is shown in lanes 1–3. Blot was probed with anti-Rpd3 antibodies.