2 TRUNCATED FORMS OF RAT INSULIN RECEPTOR-RELATED RECEPTOR

The insulin receptor-related receptor (IRR) (1271 amino acids) is expe cted to have unique functions as a novel member of the insulin recepto r family. In this paper, we report two alternatively spliced variants of rat IRR mRNA, which are predicted to encode two truncated forms of IRR, sIRR-1 (410 amino acids) and sIRR-2 (469 amino acids). The amino acid sequence of sIRR-1 is identical to the N-terminal 410-amino acid sequence of IRR. sIRR-2 has an additional 59-amino acid insertion in t he C-terminal region. Both truncated forms retain the N-terminal and c ysteine-rich domains but lack the transmembrane and intracellular tyro sine kinase domains, indicating that the truncated forms are the secre ted forms. The translation products of the truncated form mRNAs were d etected in the stomach and kidney by Western analysis. However, the ph ysiological significance of the secreted forms remains to be elucidate d.