Isolation and characterization of alpha-amylase messenger RNA from bank vole parotid glands. Evidence for two separate messenger RNAs coding for amylase and an amylase-related protein.
Bank vole saliva contains two glycogen-precipitable proteins, both of which show affinity for the alpha-amylase inhibitor cycloheptaamylose. One of these proteins, amylase, has a molecular weight of 55,000, judged from dodecylsulphate/acrylamide gel electrophoresis. The other has an apparent molecular weight of 59,000 and has no amylase activity. We report here that tryptic peptide maps as well as amino-acid composition analyses indicate extensive homology between the two proteins. We have also isolated total poly(A)-containing mRNA from amylase-rich bank vole parotid glands. These mRNAs were translated in the presence of [35S]methionine in an mRNA-dependent cell-free translation system from rabbit reticulocyte lysate. The radioactive translation products were examined by dodecylsulphate/polyacrylamide gel electrophoresis. Two major translation products with apparent molecular weights of approximately 56,500 and 60,500, respectively, were further characterized by tryptic peptide analyses. Our data indicate that the 56,500-Mr product is the biosynthetic precursor of amylase, whereas the 60,500-Mr translation product is a precursor of the 59,000-Mr amylase-like protein. Both precursors appear to contain extra peptide material, presumably as amino-terminal 'pre' or 'signal' peptides, in analogy with that found for other precursors of secretory proteins. Thus, amylase and the 59,000-Mr protein, although very similar, are translated from two separate mRNAs. These two messengers sediment in a sucrose gradient at about 17-S, corresponding to lengths of about 1,800 nucleotides.
D000596:Amino Acids / Q000032:analysis; D000681:Amylases / Q000235:genetics*; D000818:Animals; D003411:Arvicolinae; D008970:Molecular Weight; D010306:Parotid Gland / Q000032:analysis / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics* / Q000302:isolation & purification; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D000516:alpha-Amylases / Q000235:genetics*
D000596:Amino Acids; D012333:RNA, Messenger; D000681:Amylases; D000516:alpha-Amylases