Cloning and Sequence Analysis of cDNA for Rat Angiotensinogen

A mixture of tetradecamer oligodeoxyribonucleotides complementary to the codons specifying the carboxylterminal sequence, Ile-His-Pro-Phe-His, of angiotensin was chemically synthesized as two pools and used for the isolation of a cDNA clone specific for angiotensinogen from a cDNA bank of rat liver mRNA sequences. The two pools (oligo 1 and oligo 2), each containing 24 oligodeoxyribonucleotides, were first used as primers to initiate reverse transcription of rat liver mRNA. One of the pools (oligo 1) was found to prime a specific32P-labeled cDNA of approximately 160 nucleotides that contained the anticoding sequence corresponding exactly to the amino acid sequence of rat angiotensin. This cDNA, in turn, was used to rescreen cDNA clones that were isolated by initially selecting the rat liver cDNA bank by hybridization with the oligo 1 mixture. One clone thus obtained, designated pRag16, was subjected to nucleotide sequence analysis and verified to contain a nearly full-length cDNA sequence coding for rat angiotensinogen precursor. The deduced amino acid sequence indicates that the precursor molecule consists of angiotensinogen of 453 amino acid residues and a putative signal peptide of 24 amino acid residues. The predicted molecular weight and amino acid composition of angiotensinogen agree well with those determined by using the purified protein. An angiotensin moiety is located at the amino-terminal part of angiotensinogen, preceded directly by the signal peptide and followed by a large carboxyl-terminal sequence that contains two internally homologous sequences and three potential glycosylation sites.