IDENTIFICATION OF NOVEL HOMOLOGS OF MOUSE IMPORTIN-ALPHA, THE ALPHA-SUBUNIT OF THE NUCLEAR PORE-TARGETING COMPLEX, AND THEIR TISSUE-SPECIFIC EXPRESSION

Transport of karyophilic proteins into the nucleus is mediated by nucl ear localization signals (NLSs) via a multistep process, The karyophil es are recognized by the importin alpha subunit in the cytoplasm to fo rm a stable complex, termed the nuclear pore-targeting complex (PTAC). To date, three different mammalian alpha subunits (mSRP1/NPI-1, PTAC5 8/mPendulin/Rch1 and Qip1) hare been identified. In this study, we rep ort the identification of three additional mouse genes homologous to t he known alpha subunits using RT-PCR methodology and show that the mou se alpha subunits can be classified into at least three subfamilies, a lpha-P, alpha-Q and alpha-S families, each composed of closely related members (more than 80% amino acid sequence identity). These three sub families, however, have similar to 50% amino acid identity to one anot her. Northern blot analysis showed that all were differentially expres sed in various mouse tissues. These results suggest that the function of these proteins may be controlled in a tissue-specific manner and th at their combinatorial expression may play a role in differentiation a nd organogenesis. (C) 1997 Federation of European Biochemical Societie s.