asy gene is a novel apoptosis-inducing gene, but its mechanism is unclear. To investigate the mechanism of asy inducing apoptosis, a novel gene encoding ASY interacting protein (asyip) is isolated from human lung cell line (WI-38) cDNA library with yeast two-hybrid system. The asyip gene is constitutively expressed as two mRNA transcripts with the size of 1.8 and 2.7kb in various human tissues at different levels. Sequence analysis of full-length cDNA reveals that the two alternative transcripts of asyip gene contain common 5' end and different 3' end, and share a common open reading frame encoding a polypeptide of 236 amino acids. Two protein kinase C phosphorylation sites and two casein kinase II phosphorylation sites are found in ASYIP amino acid sequence. Two highly hydrophobic regions encoding potentially two transmembrane domains are present. The ASYIP protein contains a C-terminal endoplasmic reticulum retrieval signal (Lys-Lys-Lys-Ala-Glu). Immunoprecipitation assay confirmed the interaction of ASY and ASYIP in mammalian cells. Compared with asy gene, overexpression of asyip gene can inhibit growth of tumor cell Saos2 and induce cell apoptosis with a low efficiency.