A Novel Phospholipase A1with Sequence Homology to a Mammalian Sec23p-interacting Protein, p125*

p125, a mammalian Sec23p-interacting protein, exhibits sequence homology with bovine testis phosphatidic acid-preferring phospholipase A1. In this study, we identified and characterized a new homologue of p125, KIAA0725p. KIAA0725p exhibited remarkable sequence similarity with p125 throughout the entire sequence determined but lacked an N-terminal proline-rich, Sec23p-interacting region. In vitrobinding analysis showed that KIAA0725p does not bind to Sec23p. KIAA0725p possessed phospholipase A1activity preferentially for phosphatidic acid. We examined the effects of overexpression of KIAA0725p on the morphology of organelles. Overexpression of KIAA0725p, like that of p125, caused dispersion of the endoplasmic reticulum-Golgi intermediate compartment and Golgi apparatus. Different from the case of p125, overexpression of KIAA0725p resulted in dispersion of tethering proteins located in the Golgi region and caused aggregation of the endoplasmic reticulum. Our results indicate that KIAA0725p is a new member of the phosphatidic acid-preferring phospholipase A1protein family and suggest that the cellular function of KIAA0725p is different from that of p125.