Transcriptional analysis of the tet(P) operon from Clostridium perfringens

The Clostridium perfringens tetracycline resistance determinant from the 47 -kb conjugative R-plasmid pCW3 is unique in that it consists of two overlap ping genes, tetA(P) and tetB(P), which mediate resistance by different mech anisms. Detailed transcriptional analysis has shown that the inducible tetA (P) and tetB(P) genes comprise an operon that is transcribed from a single promoter, P3, located 529 bp upstream of the tetA(P) start codon. Deletion of P3 or alteration of the spacing between the -35 and -10 regions signific antly reduced the level of transcription in a reporter construct. Induction was shown to be mediated at the level of transcription. Unexpectedly, a fa ctor-independent terminator, T1, was detected downstream of P3 but before t he start of the tetA(P) gene. Deletion or mutation of this terminator led t o increased read-through transcription in the reporter construct. It is pos tulated that the TI terminator is an intrinsic control element of the tet(P ) operon and that it acts to prevent the overexpression of the TetA(P) tran smembrane protein, even in the presence of tetracycline.