A NOVEL DYNAMIN-LIKE PROTEIN ASSOCIATES WITH CYTOPLASMIC VESICLES ANDTUBULES OF THE ENDOPLASMIC-RETICULUM IN MAMMALIAN-CELLS

Dynamins are 100-kilodalton guanosine triphosphatases that participate in the formation of nascent vesicles during endocytosis, Here, we hav e tested if novel dynamin-like proteins are expressed in mammalian cel ls to support vesicle trafficking processes at cytoplasmic sites disti nct from the plasma membrane. Immunological and molecular biological m ethods were used to isolate a cDNA clone encoding an 80-kilodalton nov el dynamin-like protein, DLP1, that shares up to 42% homology with oth er dynamin-related proteins. DLP1 is expressed in all tissues examined and contains two alternatively spliced regions that are differentiall y expressed in a tissue-specific manner, DLP1 is enriched in subcellul ar membrane fractions of cytoplasmic vesicles and endoplasmic reticulu m. Morphological studies of DLP1 in cultured cells using either a spec ific antibody or an expressed green fluorescent protein (GFP)DLP1 fusi on protein revealed that DLP1 associates with punctate cytoplasmic ves icles that do not colocalize with conventional dynamin, clathrin. or e ndocytic ligands. Remarkably, DLP1-positive structures coalign with mi crotubules and, most strikingly, with endoplasmic reticulum tubules as verified by double labeling with antibodies to calnexin and Rab1 as w ell as by immunoelectron microscopy. These observations provide the fi rst evidence that a novel dynamin-like protein is expressed in mammali an cells where it associates with a secretory, rather than endocytic m embrane compartment.