Molecular cloning of multiple bovine aspartyl protease genes

Abstract

Eight bovine genomic clones have been identified as members of the aspartyl protease gene family. The clones were prepared in phage vector λ EMBL3 from Sau3AI partial digests of DNA from a single animal. Restriction maps show that seven of these clones are related and comprise at least five non-overlapping sequences. Allowing for allelic variation these probably represent three or more different genes. The nucleotide sequences show open reading frames (ORFs) corresponding closely to exons 6, 7 and 8 of human and porcine pepsin A. Comparison with other aspartyl proteases shows that these are multiple bovine pepsin A genes. The seven clones would encode at least two different but closely related forms of pepsin A. The 5′ splice site at the end of exon 7 in all seven clones is the unusual sequence GC. The eighth clone contains an ORF homologous to exon 2 of the mammalian aspartyl proteases. The corresponding amino acid sequence is more closely related to bovine chymosin than to any of the other known sequences; it may be functionally homologous to chymosin but could be a novel mammalian aspartyl protease. The intron/exon boundaries seen in both this clone and in the bovine pepsin A clones are at the same positions as found in human pepsin A, bovine chymosin and human and mouse renins, further evidence that the general structure of mammalian aspartyl protease genes has been strongly conserved.