we have identified and characterized a new mouse gene sequence, Munc18c(L), that appears closely related to the syntaxin-binding protein. Munc18c. The novel Munc18c(L) gene is comprised of 2 exons separated by a 600 by intron sequence with non-consensus donor and acceptor sites. Exons 1 and 2 of Munc18c(L) overlap with exons 1 through half of 9 of the Munc18c gene. The deduced amino acid sequence of MunC18C(L) is 271 amino acids long with homology to Munc18c protein ending at position 250. RT-PCR of murine tissues showed expression of Munc18c(L) in various tissues. RT-PCR carried out with a primer spanning the ATG codon and another one specific for the exon 2 of Mttnc18c(L) revealed two different transcripts of 0.8 and 1.4 kbp in length. Using 5 '-RACE, the start of Munc18c(L) exon 1 snatches the one predicted for Mtnc18c, but the proximal promoter differ. This first identification of Mtme18C(L) is vital in differentiating between Munc18c(L) and Munc18c and their potential roles in insulin-mediated glucose uptake. (c) 2005 Elsevier Inc. All rights reserved.