We have isolated a yeast SEC23-related clone (Msec23) from mouse fibroblast cDNA library. It has an open reading frame of 1721 bp (64% homologous to SEC23-2.3 kb) which can potentially encode a 64.7 kDa protein (61% homologous to 85.4 kDa product of SEC23). The deduced Msec23 protein (Msec23p) sequence contains three successive Ig-like domains at the N-terminus followed by amphipathic alpha-helical regions, suggesting the potential of Msec23p to interact with other protein components. Further, Msec23 is differentially expressed in mouse tissues with its high level in brain and fibroblasts.