IDENTIFICATION, CLONING, AND NUCLEOTIDE SEQUENCING OF THE ORNITHINE DECARBOXYLASE ANTIZYME GENE OF ESCHERICHIA-COLI

The ornithine decarboxylase antizyme gene of Escherichia coli was iden tified by immunological screening of an E. coli genomic library. A 6.4 -kilobase fragment containing the antizyme gene was subcloned and sequ enced. The open reading frame encoding the antizyme was identified on the basis of its ability to direct the synthesis of immunoreactive ant izyme. Antizyme shares significant homology with bacterial transcripti onal activators of the two-component regulatory system family; these s ystems consist of a ''sensor'' kinase and a transcriptional regulator. The open reading frame next to antizyme is homologous to sensor kinas es. Antizyme overproduction inhibits the activities of both ornithine and arginine decarboxylases without affecting their protein levels. Ex tracts from E. coli bearing an antizyme gene-containing plasmid exhibi t increased antizyme activity. These data strongly suggest that (i) th e cloned gene encodes the ornithine decarboxylase antizyme and (ii) an tizyme is a bifunctional protein serving as both an inhibitor of polya mine biosynthesis as well as a transcriptional regulator of an as yet unknown set of genes.