ULTRASTRUCTURAL AND BIOCHEMICAL-PROPERTIES OF THE 120-KDA FORM OF CHICK KINECTIN

Kinectin, an integral membrane protein (160 kDa), was identified as a kinesin-binding protein. Analysis of the predicted amino acid sequence of kinectin cDNA indicated an alpha-helical coiled-coil structure fro m amino acid 320 to 1310, A 120-kDa kinectin has been observed consist ently, and N-terminal sequencing showed that 232 amino acids were miss ing from the N terminus of full-length kinectin, 120-kDa kinectin was distributed in the supernatant and a low density fraction of vesicles, whereas both forms were in the high density fraction of vesicles. In the electron microscope, the 120-kDa form appeared as a linear molecul e of 133 nn in length. In hydrodynamic studies, the cytosolic 120-kDa kinectin was a dimer, Monoclonal antibody molecules (anti-kinectin BR1 60.9) bound asymmetrically to kinectin often with two antibodies/kinec tin, indicative of a parallel coiled-coil. Metabolic labeling with [H- 3]myristic acid showed that both the 120- and 160-kDa kinectin are myr istoylated in chick embryo fibroblasts, The myristoylation of 120-kDa kinectin may provide a mechanism for linking it to a low density fract ion of vesicles. Immunoprecipitation with a 160-kDa kinectin-specific antibody brought down the 120-kDa kinectin, Thus, we suggest that kine ctin is an extended parallel coiled-coil dimer, often a heterodimer.