Characterization of the hamster desmin gene: Expression and formation of desmin filaments in nonmuscle cells after gene transfer

The structural organization of the hamster gene encoding the intermediate filament (IF) protein desmin has been determined. The gene, 6.5 kb in length, contains nine exons with a total length of 2169 nucleotides. Remarkably, the intervening sequences map at positions that fully correspond to those of the vimentin gene. The derived complete primary structure for hamster desmin (468 amino acids; 53,250 daltons) reveals striking species variations in the NH 2-terminal domain of desmin. A plasmid containing the complete transcription unit of the desmin gene was transfected into hamster lens cells and into human epithelial (HeLa) cells. In both nonmuscle cell lines the desmin gene was biologically active. The synthesized desmin assembled into authentic IFs, as monitored by immunofluorescence. Double immunofluorescence staining showed that the newly formed desmin filaments colocalize with preexisting vimentin filaments, but not with preexisting keratin filaments.