Molecular cloning and nucleotide sequence analysis of the maltose-inducible porin gene ofAeromonas salmonicida

The gene for the Aeromonas salmonicida maltose-inducible porin (maltoporin) was cloned into phagemid pTZ18R in two restriction fragments, 0.6-kb PstI/KpnI and 1.7-kb SphI, of genomic DNA and their nucleotide sequences were determined. Open reading frames of 1329 and 1335 bp translated into sequences of 443 and 445 amino acids, with a 23 or 25 amino acid signal sequence and a 420 amino acid mature protein of molecular mass 46424 Da. Putative ribosome binding sites, AGGA and GGGAA, occurred 9 bp upstream of two possible ATG initiation codons. The A. salmonicida gene product showed a high degree of similarity with Escherichia coli LamB, and codon usage was very similar to that of another A. salmonicida outer membrane protein but markedly different from those of extracellular proteins.