Determination of functional regions of p125, a novel mammalian Sec23p-interacting protein

The Sec23p-Sec24p complex is a component of coat protein II-coated vesicles involved in protein export from the endoplasmic reticulum. We previously i dentified a novel Sec23p-interacting protein, p125, which consists of 1000 amino acids and comprises a proline-rich region and a phospholipase A, homo logy region. p125, when ectopically expressed in cultured cells, localizes to endoplasmic reticulum-Golgi intermediate regions. In the present study w e showed that expressed p125 principally colocalizes with p115 and GM130, b oth of which are involved in vesicle tethering to Golgi membranes. Next, we determined the functional regions of p125 by expressing a p125 series with deletions. The results showed that the proline-rich region (residues 135-2 59) is responsible for the binding to Sec23p. For the correct localization of p125, a region (residues 135-1000) comprising both the proline-rich and phospholipase A, homology regions was required. (C) 2000 Academic Press.