Several classes of cytoplasmic proteins have been found to interact specifically with the carboxyl-terminal cytoplasmic region of the angiotensin II type 1 (AT(1)) receptor to regulate different aspects of AT(1) receptor physiology. The murine Angiotensin II Receptor-Associated Protein (Agtrap) is a new member of them. We have recently cloned a new human gene cDNA that codes for a homolog of the murine Agtrap protein from a human fetal brain cDNA library. The deduced polypeptide product of the cDNA is 22 kDa in size, and its DNA and amino acid sequences are 85 and 77% identical to those of the mouse Agtrap gene, respectively. Hence we have named it the human Angiotensin II Receptor-Associated Protein (AGTRAP) gene. The mRNA of AGTRAP was most abundantly expressed in kidney, heart, pancreas and thyroid. Using the yeast two-hybrid screening of a human fetal brain cDNA library, we have identified a new interaction partner of the human AGTRAP protein, RACK1 (Receptor of Activated Protein C Kinase). The AGTRAP-RACK1 interaction was confirmed by GST fusion protein pull-down assays, co-immunoprecipitation and surface plasmon resonance. We suggest that the AGTRAP-RACK1 interaction may help to recruit signaling complex to the AT(1) receptor to affect AT(1) receptor signaling.