RT PCR results confirm inhibition of transcription by IS 1 insertion. (A) Gel electrophoresis of RT-PCR products made from RNA prepared from cells harboring pCTXVP60IS1 or pCTXVP60, as indicated. Two parallel experiments were performed with each sample. Primers ORFstart and ORFstop were used in lanes 1-4, and control primers groL1 and groL2 in lanes 5-8. White arrows mark the expected sizes of the respective PCR products. (B) Map indicating the position of IS1, orf238 and PCR primers relative to the ctxvp60 gene.