THE DROSOPHILA LETHAL(2)GIANT LARVAE TUMOR-SUPPRESSOR PROTEIN FORMS HOMO-OLIGOMERS AND IS ASSOCIATED WITH NONMUSCLE MYOSIN-II HEAVY-CHAIN

Inactivation of the Drosophila lethal(2)giant larvae (l(2)gl) gene cau ses malignant tumors in the brain and the imaginal discs and produces developmental abnormalities in other tissues, including the germline, the ring gland and the salivary glands. Our investigations into the l( 2)gl function have revealed that the gene product, or p127 protein, ac ts as a cytoskeletal protein distributed in both the cytoplasm and on the inner face of lateral cell membranes in a number of tissues throug hout development. To determine whether p127 can form oligomers or can stably interact with other proteins we have analyzed the structure of the cytosolic form of p127. Using gel filtration and immunoaffinity ch romatography we found that p127 is consistently recovered as high mole cular weight complexes that contain predominantly p127 and at least te n additional proteins. Blot overlay assays indicated that p127 can for m homo-oligomers and the use of a series of chimaeric proteins made of segments of p127 fused to protein A, which alone behaves as a monomer , showed that p127 contains at least three distinct domains contributi ng to its homooligomerization. Among the proteins separated from the i mmune-purified p127 complexes or isolated by virtue of their affinity to p127, we identified one of the proteins by microsequencing as nonmu scle myosin II heavy chain. Further blot overlay assay showed that p12 7 can directly interact with nonmuscle myosin II. These findings confi rm that p127 is a component of a cytoskeletal network including myosin and suggest that the neoplastic transformation resulting from l(2)gl gene inactivation may be caused by the partial disruption of this netw ork.