Fm. Lu et Kf. Chak, 2 OVERLAPPING SOS-BOXES IN COLE-OPERONS ARE RESPONSIBLE FOR THE VIABILITY OF CELLS HARBORING THE COL-PLASMID, MGG. Molecular & general genetics, 251(4), 1996, pp. 407-411
In this study, oligonucleotide-directed site-specific mutagenesis was
used to change the consensus sequences of the LexA binding motifs in e
ither one of the two SOS-boxes of the Co1E7 operon. The results indica
ted that both mutants produced larger amounts of colicin than cells ha
rboring the wild-type Co1E7 plasmid. This finding would imply that two
biologically functional SOS boxes exist in the Co1E7 operon. In the n
on-induced state, no lysis of cells harboring wild-type plasmids occur
red at 37 degrees C, whereas, cells harboring recombinant plasmids con
taining either one of the mutated SOS boxes underwent lysis within 100
min under the same conditions. This result indicated that adaptation
of two SOS boxes of the Co1E operon would obviously tightly control th
e expression of Co1E operons. In such a way that it may prevent excess
ive expression of the lysis (cel) gene, thus safeguard the host cells
from being lysed in ordinary living conditions.