Molecular identification of two novel Munc-18 isoforms expressed in non-neuronal tissues.
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.
Tellam
J T
JT
Center for Molecular Biology and Biotechnology, University of Queensland, St Lucia, Australia.
McIntosh
S
S
James
D E
DE
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D015723:Gene Library; D014644:Genetic Variation; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D009928:Organ Specificity; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012984:Software; D013572:Synaptic Vesicles / Q000378:metabolism; D013737:Testis / Q000378:metabolism*; D033921:Vesicular Transport Proteins
D017931:DNA Primers; D018076:DNA, Complementary; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C497938:Stxbp1 protein, mouse; C497941:Stxbp2 protein, mouse; C497943:Stxbp3 protein, mouse; C497944:Stxbp3 protein, rat; D033921:Vesicular Transport Proteins