Molecular Identification of Two Novel Munc-18 Isoforms Expressed in Non-neuronal Tissues

doi:10.1074/jbc.270.11.5857

Molecular Identification of Two Novel Munc-18 Isoforms Expressed in Non-neuronal Tissues (*)

From the Center for Molecular Biology and Biotechnology and Department of Physiology and Pharmacology, University of Queensland, St Lucia, 4072, QLD, Australia

^¶ Wellcome Research Fellow. To whom correspondence should be addressed. Tel.: 61-7-365-4986; Fax: 61-7-365-4388.

Abstract

Munc-18, also known as n-Sec1 or rbSec1, is a syntaxin-binding protein thought to play a role in regulating synaptic vesicle exocytosis. Although a gene family of syntaxins has been identified, only a limited subset bind to Munc-18. This implicates the existence of other mammalian Munc-18 homologues that may be involved in a range of vesicle transport reactions. The purpose of the present study was to identify other members of the Munc-18 family by cDNA cloning. Three distinct Munc-18 isoforms, Munc-18a, previously identified in neuronal tissue, and two novel isoforms, Munc-18b and Munc-18c, were isolated from a 3T3-L1 adipocyte cDNA library by screening with a rat brain Munc-18 DNA probe. Munc-18a is identical to Munc-18 and by Northern analysis is expressed predominantly in brain and to a lesser extent in testis and 3T3-L1 cells. Munc-18b is 62% identical to Munc-18 at the amino acid level and is expressed in testis, intestine, kidney, rat adipose tissue, and 3T3-L1 cells. Munc-18c is 51% identical to Munc-18 and is ubiquitously expressed. It is likely, based on these findings, that unique Munc-18/syntaxin interactions may play an important role in generating a combinatorial mechanism for the regulation of vesicle transport in mammalian cells.

Footnotes

↵^§ National Health and Medical Research Council (Dora Lush) postgraduate scholar.
↵* This work was supported by the National Health and Medical Research Council of Australia. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(TM)/EMBL Data Bank with accession number(s) U19520 [GenBank](munc-18b gene) and U19521 [GenBank](munc-18c gene).
↵¹ The abbreviations used are:

SNAREs

soluble N-ethylmaleimide-sensitive factor attachment protein receptors

V-SNARE

vesicle membrane SNARE

T-SNARE

target membrane SNARE

Munc-18

mammalian homologue of unc-18

kb

kilobase(s)

bp

base pair(s).
- Received November 29, 1994.
- Revision received January 12, 1995.