Inbred strains of mice have been divided into two distinct phenotypic groups having different levels of renin activity regulated by androgen in the submaxillary gland (SMG). Strains carrying the Rnrs allele of the renin gene regulator, located on chromosome 1, have a high level of renin activity; strains carrying the Rnrb allele have a low level of renin activity. The level of SMG renin activity correlates with the level of renin mRNA. We have analyzed, by Southern blot hybridization, the organization of renin genes in both strains. Strains carrying the Rnrb allele, such as BALB/c or C57 Bl/6, or CH3 mice, have one renin structural gene per haploid genome, while those having the Rnrs allele, such as AKR or Swiss mice, have two renin genes. We have also identified renin genes in mice belonging to different biochemical groups: Mus spretus has one renin gene while M. vrania and M. musculus brevirostris have two renin genes.

Overlapping recombinant clones that appear to encompass the entire renin gene, named Ren 1, have been isolated from a library of BALB/c mouse genomic DNA fragments. Based on restriction endonuclease mapping and DNA sequence analysis, Ren 1 spans 9.6 kb and contains nine exons interrupted by eight intervening sequences of highly variable size. The first exon, encoding the signal peptide of preprorenin, is separated from the eight following exons by a 3-kb intron. These eight exons are organized into two clusters of four separated by a 2-kb intron. DNA stretches encoding the aspartyl residues, which are part of the active site of renin, are located at homologous positions in both clusters. Our results show that aspartyl protease genes have arisen by duplication and fusion of an ancestral gene containing five exons. The estimated date of the duplication event of the mouse renin genes Ren 1 and Ren 2 is discussed.Key words: kidney renin/protein glycosylation/rate of divergence/exon-intron boundaries Introduction Aspartyl protease represents one of the protein families most completely characterized by primary amino acid sequence and crystallographic studies. The aspartyl proteases active site contains two aspartate residues localized in two short amino acid stretches with sequence homology to one another, and separated by a distance of about half of the polypeptide chain (Sepulveda et al., 1975). Aspartyl proteases such as penicellopepsin have a bilobal structure in which the two lobes are related by a 2-fold symmetry axis (Hsu et al., 1977). These observations have led to a hypothesis that aspartyl protease genes have evolved by duplication and fusion of an ancestral gene coding for a 15 000 -20 000 dalton polypeptide having a fold similar to that of one lobe of pepsin (Tang et al., 1978).In contrast to the other aspartyl proteases, renin has an optimal activity at neutral pH and a substrate specificity restricted to the cleavage of the prohormone angiotensinogen. The primary source of renin is the kidney where its concentration is extremely low. However, in some mouse strains, high levels of renin activity are found in the submaxillary gland (SMG) of males (Wilson et al., 1977). The amino acid sequence of the SMG renin has been recently reported (Panthier et al., 1982a;Misono et al., 1982). Comparison of the amino acid sequence of renin and pepsin shows -420Wo homology. The two most homologous regions are those surrounding the active sites aspartates. These results strongly suggest that renin and pepsin genes derive from a common ancestor.

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A DNA sequence complementary to the entire coding part of a mouse gamma 2a immunoglobulin heavy chain mRNA isolated from a myeloma producing a levan binding protein (UPC 10), has been cloned in the PstI site of pBR 322. Transformants containing sequences complementary to purified gamma 2a heavy chain mRNA were selected. One transformant, pG2a-10-21, containing a 1750 nucleotide insert, has been characterized by hybrid-arrested translation and purification of gamma 2a heavy chain mRNA on DNA-DBM cellulose filters. Restriction enzyme analysis and partial sequencing demonstrate that the pG2a-10-21 contains the complete structural sequence for the gamma 2a heavy chain and predicts the sequence of a 18 amino acid hydrophobic amino terminal extra piece segment.

Two distinct phenotypic groups of inbred strains of mice, with different amounts of submaxillary gland (SMG) renin have been described. We have previously shown that strains with high levels of SMG renin, such as Swiss or AKR mice, have two renin genes, Rn1 and Rn2, per haploid genome, while strains with low levels of SMG, such as BALB/c or C57Bl/6, have only one renin gene. We now report the molecular cloning of cDNA copies of Swiss mouse kidney renin mRNA and present nucleotide sequence data of the recombinant clones. Comparison of these sequences with the sequence of Swiss mouse SMG renin mRNA we have previously reported, demonstrates that Swiss mice express the two non‐allelic genes, Rn1 and Rn2.