CLONING, TISSUE EXPRESSION, AND CHROMOSOMAL LOCALIZATION OF THE MOUSEIRS-3 GENE

Insulin receptor substrate (IRS) proteins are key regulators of basic functions such as cellular growth and metabolism. They provide an inte rface between multiple receptors and a complex network of intracellula r signaling molecules. Two members of this family (IRS-1 and IRS-2) ha ve been identified previously. In this investigation, we analyzed a mo use expressed sequence tag clone that proved to be a new member of the IRS family. Sequence analysis of this clone and comparison with the s equences deposited in GenBank demonstrates this protein may be the mur ine homolog of rat IRS-3, recently purified and cloned from rat adipoc ytes. Accordingly, we have named our protein mouse IRS-3. The expresse d sequence tag clone contains the complete coding sequence of 1485 bp, encoding a protein of 495 amino acids. Sequence alignment with the ot her members of the IRS family shows that this protein contains pleckst rin homology and phosphotyrosine-binding domains that are highly conse rved. In addition, there is conservation of many tyrosine phosphorylat ion motifs responsible for interactions with downstream signaling mole cules containing SH2 domains. The murine IRS-3 messenger RNA (2.4 kilo bases in length) is expressed in many tissues, with highest levels in liver and lung. Mouse IRS-3 is highly expressed in the first part of t he embryonic life, when IRS-1 messenger RNA is barely detectable. Unli ke the genes encoding IRS-1 and IRS-2, the IRS-3 gene contains an intr or (344 bp in length) in the region between the pleckstrin homology an d the phosphotyrosine-binding domains. Fluorescent in situ hybridizati on localized the mouse IRS-3 gene on the telomeric region of chromosom e 5G2. Cloning of the murine IRS-3 gene will make it possible to apply genetic approaches to elucidate the physiological role of this new me mber of the IRS family of proteins.