Structure and regulation of the AMP nucleosidase gene (amn) from Escherichia coli.

The gene for AMP nucleosidase from Escherichia coli (amn) has been sequenced and characterized. The gene codes for a transcript of 1.7 +/- 0.2 kb, and the open reading frame corresponds to a protein of 483 amino acids (Mr = 53848). Amino acid sequences from tryptic peptides of AMP nucleosidase, N-terminal amino acid analysis, and the amino acid composition confirm the gene assignment and the open reading frame of amn. Primer extension studies determined the 5'-end of the amn transcript. The 5'-regulatory region contains overlapping sequences with similarity to the consensus sequences for binding cAMP receptor protein and inorganic phosphate repressor protein. Addition of exogenous cAMP to E. coli deficient in adenylate cyclase resulted in a 3-fold increase in AMP nucleosidase activity. Growth of E. coli on limiting phosphate resulted in an 8-fold increase in the production of AMP nucleosidase. The amn gene was expressed in AMP nucleosidase deficient strains of Azotobacter vinelandii and E. coli. A pUC-amn construct is described that causes approximately 20% of the total protein in E. coli to be produced as AMP nucleosidase. Comparison of the amino acid sequence for AMP nucleosidase with that for yeast AMP deaminase indicates a region in which six of eight amino acids are identical but no other overall homology. The amino acid sequence showed poor agreement with consensus sequences for adenylate binding sites even though the enzyme is known to have a catalytic site for AMP and regulatory sites for MgATP and phosphate.

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