Identification of four different forms of syntaxin 3.

cDNAs for four different forms of syntaxin 3 were cloned from a mouse brain cDNA library, and the proteins encoded by these clones were named syntaxin 3A (previous syntaxin 3), 3B, 3C and 3D. Syntaxin 3B contained a different sequence in the carboxyl terminal region from that of syntaxin 3A. The amino terminal region of syntaxin 3C contained an 18 amino acid sequence instead of a 34 amino acid sequence present in syntaxins 3A and 3B. Syntaxin 3D consisted of only 86 amino acids and lacked any putative transmembrane segments. These forms of syntaxin 3 are probably generated by alternative splicing of the primary transcript of syntaxin 3 gene. Cytoplasmic portions of syntaxins 3A and 3B but not of syntaxin 3C or 3D bound to Munc-18/n-sec1.