Gene expression of ampicillin resistance transposons, Tn2601 and Tn2602

To establish the mode of gene expression specified by transposon, we investigated the correlation among the homology of the DNA sequence, the extent of transposon-specific transcription, the specific activity of penicillinase (PCase) per cell, and the transposition frequency by using two ampicillin resistance transposons (TnAs), Tn2601 and Tn2602. Although both the TnAs specify the so-called type I PCase, Tn2602 always conferred 10- to 20-fold higher PCase activity per cell than Tn2601 regardless of the kind of replicon carrying TnA. The transposition freuency of Tn2602 also was 8 to 50 times higher than that of Tn2601 in all combinations of donor and recipients plasmids examined. As a result, the transposability expressed by the TnA was thought to correlate with the productivity of PCase in the cell specified by the corresponding TnA. The level of TnA-specific transcription of Tn2602 was noticeably higher than that of Tn2601, whereas the two TnAs shared a high degree (more than 90%) of DNA sequence homology. These results suggest that the difference in rates of transcription of the two transposons plays a key role in determining the difference in the productivity of PCase and the transposition-protein(s) of Tn2601 and Tn2602.