DISTINCT REGIONS SPECIFY THE TARGETING OF OTEFIN TO THE NUCLEOPLASMICSIDE OF THE NUCLEAR-ENVELOPE

Otefin is a 45-kDa nuclear envelope protein with no apparent homology to other known proteins. It includes a large hydrophilic domain, a sin gle carboxyl-terminal hydrophobic sequence of 17 amino acids, and a hi gh content of serine and threonine residues. Cytological labeling loca ted otefin on the nucleoplasmic side of the nuclear envelope. Chemical extraction of nuclei from Drosophila embryos revealed that otefin is a peripheral protein whose association with the nuclear envelope is st ronger than that of lamin. Deletion mutants of otefin were expressed i n order to identify regions that direct otefin to the nuclear envelope . These experiments revealed that the hydrophobic sequence at the carb oxyl terminus is essential for correct targeting to the nuclear envelo pe, whereas additional regions in the hydrophilic domain of otefin are required for its efficient targeting and stabilization in the nuclear envelope.