SYNTAXIN-16, A PUTATIVE GOLGI T-SNARE

Members of the syntaxin family of integral membrane proteins have rece ntly been implicated as vesicle receptors on target membranes, corespo nsible for the specificity of intracellular membrane traffic. So far, only a small number of different mammalian syntaxins have been identif ied. Here we report the cloning of three new human syntaxin cDNAs, pre sumably originating from alternative splicing of the same transcript. Syntaxin-16A and syntaxin-16B are identical, except that the latter co ntains an insertion of 21 amino acid residues. Syntaxin-16C is a trunc ated version of syntaxin-16A, lacking the C-terminal coiled-coil and h ydrophobic regions characteristic for syntaxins. Database searches ide ntified putative yeast, plant and nematode homologues of syntaxin-16, indicating that this protein is conserved through evolution, and synta xin-16 belongs to a new subgroup of syntaxins. Epitope-tagged syntaxin -16A and syntaxin-16B were found to colocalize with the Golgi marker b eta-COP, while syntaxin-16C was found in the cytosol. Syntaxin-16A ass ociates posttranslationally with microsomes, and appears to be transpo rted to the Golgi via the endoplasmic reticulum. The three syntaxin-16 forms may have differential roles in intracellular trafficking.