SEQUENCE OF A CLASS-E TETRACYCLINE RESISTANCE GENE FROM ESCHERICHIA-COLI AND COMPARISON OF RELATED TETRACYCLINE EFFLUX PROTEINS

We determined the nucleotide sequence of the class E tetA gene on plas mid pSL1456 from Escherichia coli SLH1456A. The deduced amino acid seq uence of the class E TetA protein shows 50 to 56% identity with the se quences of five related TetA proteins (classes A through D and G). Hyd rophobicity profiles identify 12 putative transmembrane segments with similar boundaries in all six TetA sequences. The N-terminal alpha dom ain of the six sequences is more highly conserved than the C-terminal beta domain; the central hydrophilic loop connecting the alpha and bet a domains is the least conserved region. Amino acid residues that have been shown to be important for class B (Tn10) TetA function are conse rved in all six TetA sequences. Unlike the class B tetA gene, the clas s D and E tet.4-genes do not exhibit a negative gene dosage effect whe n present on multicopy plasmids derived from pACYC177.