H. Yigit et Ws. Reznikoff, ESCHERICHIA-COLI DNA TOPOISOMERASE-I AND SUPPRESSION OF KILLING BY TN5 TRANSPOSASE OVERPRODUCTION - TOPOISOMERASE-I MODULATES TN5 TRANSPOSITION, Journal of bacteriology (Print), 180(22), 1998, pp. 5866-5874
Tn5 transposase (Tnp) overproduction is lethal to Escherichia coli. Th
e overproduction causes cell filamentation and abnormal chromosome seg
regation. Here we present three lines of evidence strongly suggesting
that Tnp overproduction killing is due to titration of topoisomerase I
. First, a suppressor mutation of transposase overproduction killing,
stkD10, is localized in topA (the gene for topoisomerase I). The stkD1
0 mutant has the following characteristics: first, it has an increased
abundance of topoisomerase I protein, the topoisomerase I is defectiv
e for the DNA relaxation activity, and DNA gyrase activity is reduced;
second, the suppressor phenotype of a second mutation localized in rp
oH, stkA14 (H. Yigit and W. S. Reznikoff, J. Bacteriol. 179:1704-1713,
1997), can be explained by an increase in topA expression; and third,
overexpression of wild-type topA partially suppresses the killing. Fi
nally, topoisomerase I was found to enhance Tn5 transposition up to 30
-fold in vivo.