GENE-TRANSFER OF A PART OF A BETA-LACTAMASE GENE

Beta-Lactamase is an enzyme which catalyzes the hydrolysis of the beta-lactam ring of penicillins and cephalosporins. By similarity analysis of amino acid sequences in a database, the amino acid sequence deduced from the nucleotide sequence of the upstream region of cytochrome c oxidase subunit II from Paracoccus denitrificans was found to have an unusually high score of homology to that of a portion of beta-lactamases from Gram-negative bacteria. Furthermore, the nucleotide sequences corresponding only to this region had a very high score of similarity among them. The phylogenetic tree constructed on the basis of the amino acid sequences was in accord with that constituted on the 5S rRNA's. Moreover, the molar G + C contents and the codon usage were similar to those in their respective bacteria. It is suggested, therefore, that the nucleotide sequence in P. denitrificans was positioned by a transfer of a part of a beta-lactamase gene formed as a result of gene duplication or it was formed by a deletion of the essential region of the beta-lactamase gene, although no beta-lactamase gene has been yet detected in P. denitrificans.