The tetracycline resistance determinants of RP1 and Tn1721: nucleotide sequence analysis.

Nucleotide sequences of the homologous tetracycline resistance (tet) determinants of plasmid RP1 and transposon Tn1721 have been determined. Two open reading frames of divergent polarity have been assigned to a regulatory gene (tetR) and a gene encoding a resistance protein (tetA). The intercistronic region contains appropriate regulatory and transcription signals. The tetR gene can code for a protein of 216 amino acids (deduced mol.wt. 23,288) and the tetA gene for a protein of 399 amino acids (deduced mol. wt. 42,205). Based on the deduced amino acid sequence, the tetA proteins of RP1/Tn1721 are 78% homologous with that of pBR322 and 45% homologous with that of Tn10. We conclude that a single tetA gene mediates resistance in each of these tet determinants.