Abstract
We have identified a human cDNA that is homologous to the chicken kinectin, a putative receptor for the organelle motor kinesin. The human cDNA clone hybridized to a single 4.6-kb mRNA species that codes for a protein of 156 kDa molecular mass. The predicted primary translation product contains an N-terminal transmembrane helix followed by a bipartite nuclear localization sequence and two further C-terminal leucine zipper motifs. In addition, the aminoacid sequence revealed a large region (327-1362) of predicted alpha-helical coiled coils. A monoclonal antibody CT-1 raised against a GST-kinectin fusion protein produced a perinuclear, endoplasmic reticulum-like staining pattern in diverse cell types from different species, indicating evolutionary conservation. Monoclonal antibody CT-1 and anti-chicken kinectin antibodies cross-reacted both in Western blotting and immunoprecipitation with a 160-kDa protein, confirming the antigenic identity of this 160-kDa protein with chicken kinectin. Epitope tagging studies revealed that the nuclear localization sequence motif of kinectin is not functional. Furthermore, a truncated kinesin cDNA lacking the N-terminal hydrophobic domain revealed a nonspecific cytoplasmic staining pattern. Together the data suggest that kinectin is an integral membrane protein anchored in the endoplasmic reticulum via a transmembrane domain.