Nuclear membrane vesicle targeting to chromatin in a Drosophila embryo cell-free system

A Drosophila cell-free system was used to characterize proteins that are required for targeting vesicles to chromatin and for fusion of vesicles to form nuclear envelopes. Treatment of vesicles with 1 M NaCl abolished their ability to bind to chromatin. Binding of salt-treated vesicles to chromatin could be restored by adding the dialyzed salt extract. Lamin Dm is one of the peripheral proteins whose activity was required, since supplying interphase lamin isoforms Dm₁ and Dm₂ to the assembly extract restored binding. As opposed to the findings in Xenopus, okadaic acid had no affect on vesicle binding. Trypsin digestion of the salt-stripped vesicles eliminated their association with chromatin even in the presence of the dialyzed salt extract. Once vesicles attached to chromatin surface, fusion events took place that were found to be sensitive to guanosine 5'-[-γ-thio]triphosphate (GTPγS). These chromatin-attached vesicles contained lamin Dm and otefin but not gp210. Thus, these results show that in Drosophila there are two populations of nuclear vesicles. The population that interacts first with chromatin contains lamin and otefin and requires both peripheral and integral membrane proteins, whereas fusion of vesicles requires GTPase activity.