CLONING AND NUCLEOTIDE-SEQUENCE OF THE DNA GYRASE GYRA GENE FROM THE FISH PATHOGEN AEROMONAS-SALMONICIDA

The DNA gyrase gvrA gene from the fish pathogen Aeromonas salmonicina 2148/89 was cloned, and the nucleotide sequence was determined. An ope n reading frame of 2,766 nucleotides was identified and was found to e ncode a protein of 922 amino acids with a calculated molecular mass of 101.1 kDa. The derived amino acid sequence shared a high degree of id entity with other DNA gyrase A proteins, in particular, with other gra m-negative GyrA sequences. When the amino acid sequence of A. salmonic ida GyrA was compared with that of Escherichia coli GyrA, a number of conserved residues were present at identical coordinates, including th e catalytic Tyr residue at position 122 (Tyr-122) and residues whose s ubstitution confers quinolone resistance, notably, Ser-83, Ala-67, Gly -81, Asp-87, Ala-84, and Gln-106. An intragenic region corresponding t o 48 amino acids, which is not present in E. coli or other bacteria, w as identified in the C-terminal part of A. salmonicina GyrA. This intr agenic region shared sequence identity with various DNA-binding protei ns of both prokaryotic and eukaryotic origins.