Cloning and sequence analysis of the arginine deiminase gene from Mycoplasma arginini

Arginine deiminase from Mycoplasma arginini was purified. The purified enzyme has a molecular weight of 46,000 daltons as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Its specific activity (20 units/mg protein) and amino acid composition showed a strong similarity to that of the Mycoplasma arthritidis arginine deiminase. The amino acid sequences of the N-terminal region and three internal peptides generated by enzymatic cleavage of the purified protein were determined. Using a synthetic oligonucleotide mixture complementary to part of the determined N-terminal amino acid sequence, the gene coding for arginine deiminase was isolated from a phage library. A nucleotide sequence of 2189 bp encoding the gene was determined. An open reading frame (ORF) contained the amino acid sequences corresponding to the determined N-terminal region and the three internal peptides of arginine deiminase. Thus it was concluded that this ORF encoded the arginine deiminase, a 385 amino acid polypeptide (mol.wt. 43,900 daltons). The three tryptophan residues in the sequenced peptides align with UGA codons in the nucleotide sequence, indicating that the nonsense codon UGA is used as a tryptophan codon in M. arginini.