78% of mutant larvae reach third instar; development delayed, and larvae never pupariate; rather they remain alive on surface of food for up to 22 days. Larvae form melanotic masses. Imaginal disc growth retarded and development abnormal, with substantial cell death; growth rate of mutant discs, but not their ability to differentiate, partially restored when transplanted into normal larval host; mutant larvae defective in support of growth of implanted wild-type discs, but do not prevent their subsequent differentiation upon retransplantation into normal larvae. Homozygous mutant clones in a wild-type background were induced at control frequencies; however, sizes of mutant clones produced earlier, but not those produced later, were smaller than control clones; differentiation of cuticular elements normal in small clones, but in large thoracic clones produced in a M background cuticular development abnormal (Pentz and Shearn). Ganglion mitosis normal according to Gatti and Baker (1989, Genes Dev. 3: 438-53), disturbed according to Pentz. l(3)SG5626 homozygotes lethal when raised at 27 but survive as fertile adults when reared at 20; shifting such adult females to 27 demonstrates that l(3)SG56 is a maternal-effect lethal and a female sterile; egg production decreases with time, and those eggs that are produced exhibit abnormal cellularization and fail to hatch; temperature effect reversable by shift down. Two-dimensional gel electrophoresis analysis of proteins from mutant tissue at restrictive vs. permissive temperatures shows reduction in levels of three proteins and a concommitant increase of three related proteins; two other proteins are absent from mutant tissue at restrictive temperatures; mutant postulated to be defective in post-translational modification of a small subset of proteins crucial to normal cell division, cell motility, and formation of adult hairs and bristles (Cheney, et al.).