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), Tn
2601 and Tn
2602. Although both the TnAs specify the so-called type I PCase, Tn
2602 always conferred 10-to 20-fold higher PCase activity per cell than Tn
2601 regardless of the kind of replicon carrying TnA. The transposition frequency of Tn
2602 also was 8 to 50 times higher than that of Tn
2601 in all combinations of donor and recipient 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 Tn
2602 was noticeably higher than that of Tn
2601, 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 Tn
2601 and Tn
2602.
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