Primary structure and assignment to chromosome 6 of three related rat genes encoding liver serine protease inhibitors

Three closely related SPI genes which encode highly homologous proteins of the serine protease inhibitor family secreted by rat liver (SPI-1, SPI-2 and SPI-3), were isolated from genomic libraries and sequenced, totally (SPI-2) or partially (SPI-1 and SPI-3). These genes all map on rat chromosome 6. Each of them spans about 10 kb and contains five exons separated by four introns, located at equivalent positions. S1 mapping analysis indicated that initiation of transcription occurs at the same position (tsp) in each of the three genes. In vitro transcription experiments demonstrated the presence of promoter elements upstream from the putative tsp. Detailed analysis of 5'-flanking sequences in the three SPI revealed major differences. A high degree of identity (70%) was found within a 350-bp region preceding the 'cap' site, with the exception of a 42-bp spacer, which was only found in SPI-3. Upstream from that point, SPI-1 and SPI-2 sequences remain largely homologous over at least 1 kb but completely diverge from the corresponding sequence in SPI-3. This may, at least partly, account for the differential regulation of the three SPI observed during acute inflammation and upon hypophysectomy.