A novel 913-amino acid protein, ␥-aminobutyric acid type A (GABA A ) receptor interacting factor-1 (GRIF-1), has been cloned and identified as a GABA A receptorassociated protein by virtue of its specific interaction with the GABA A receptor ␤2 subunit intracellular loop in a yeast two-hybrid assay. GRIF-1 has no homology with proteins of known function, but it is the rat orthologue of the human ALS2CR3/KIAA0549 gene. GRIF-1 is expressed as two alternative splice forms, GRIF-1a and a C-terminally truncated form, GRIF-1b. GRIF-1 mRNA has a wide distribution with a major transcript size of 6.2 kb. GRIF-1a protein is only expressed in excitable tissues, i.e. brain, heart, and skeletal muscle major immunoreactive bands of M r ϳ 115 and 106 kDa and, in muscle and heart only, an additional 88-kDa species. When expressed in human embryonic kidney 293 cells, GRIF-1a yielded three immunoreactive bands with M r ϳ 115, 106, and 98 kDa. Co-expression of GRIF-1a and ␣1␤2␥2 GABA A receptors in mammalian cells revealed some co-localization in the cell cytoplasm. Anti-FLAGagarose specifically precipitated GRIF-1 FLAG and GABA A receptor ␤2 subunits from human embryonic kidney 293 cells co-transfected with GRIF-1a FLAG and ␤2 subunit clones. Further, immobilized GRIF-1-(8 -633) specifically precipitated in vitro GABA A receptor ␣1 and ␤2 subunit immunoreactivities from detergent extracts of adult rat brain. The respective GABA A receptor ␤2 subunit/GRIF-1 binding domains were mapped using the yeast two-hybrid reporter gene assays. A possible role for GRIF-1 as a GABA A receptor ␤2 subunit trafficking factor is proposed.

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