LOCALIZATION AND POSTTRANSLATIONAL MODIFICATIONS OF OTEFIN, A PROTEINREQUIRED FOR VESICLE ATTACHMENT TO CHROMATIN, DURING DROSOPHILA-MELANOGASTER DEVELOPMENT

Otefin is a peripheral protein of the inner nuclear membrane in Drosop hila melaaogaster: Here we show that during nuclear assembly in vitro, it is required for tile attachment of membrane vesicles to chromatin. With the exception of sperm cells, otefin colocalizes with lamin Dm(0 ) derivatives in situ and presumably in Five and is present in ail som atic cells examined during the different stages of Drosophila developm ent, In the egg chamber, otefin accumulates in the cytoplasm, in the n uclear periphery, and within the nucleoplasm of the oocyte in a patter n similar to that of lamin Dm(0), derivatives. There is a relatively l arge nonnuclear pool of otefin present from stages 6 to 7 of egg chamb er maturation through 6 to 8 h of embryonic development at 25 degrees C, In this pool, otefin is peripherally associated with a fraction con taining the membrane vesicles, This association is biochemically diffe rent from the association of otefin with the nuclear envelope, Otefin is a phosphoprotein in vivo and is a substrate for in vitro phosphoryl ation bf cdc2 kinase and cyclic AMP-dependent protein kinase, A major site for cdc2 kinase phosphorylation in vitro was mapped to serine 36 of otefin, Together, our data suggest an essential role for otefin in the assembly of the Drosophila nuclear envelope.