VPS35 is a component of a large multimeric complex, termed the retromer complex, involved in retrograde transport of proteins from endosomes to the trans-Golgi network. The close structural similarity between the yeast and human proteins that make up this complex suggests a similarity in function. Expression studies in yeast and mammalian cells indicate that this protein interacts directly with VPS35, which serves as the core of the retromer complex. The SSEC-26 transcript was abundant in the unfertilized egg and also actively transcribed from the newly formed zygotic genome. On the basis of its expression in eggs and embryos, this mouse gene was named Mem3 (maternal-embryonic-3). The deduced amino acid sequence of Mem3 resembles that of the yeast VPS35 protein in 2 separate domains.