Frequency of T7 RNA polymerase resistance and loss of sitA in RecA+ and RecA S. flexneri

Strain (genotype)Avg frequency of T7 polymerase resistanceaRange% of resistant isolates with deletion of:
T7 promotersbsit genesc
SM100/pAR1219 (wild type)2.7 × 10−41.0 × 10−4-4.1 × 10−410075
SM166/pAR1219 (sit::cam)8.9 × 10−31.6 × 10−3-5.6 × 10−410060
SM160/pAR1219 (recA::cam)2.9 × 10−52.0 × 10−5-5.7 × 10−600
  • a Strains were grown in LB broth and plated on medium containing IPTG to induce expression of T7 polymerase from pAR1219. The frequency is the ratio of colonies on IPTG-containing medium to the number of colonies from the same culture plated on medium without IPTG. The average and range of values for 4 to 10 separate experiments are shown.

  • b A minimum of 10 individual colonies was selected and tested by PCR with primers in the T7 promoters.

  • c Individual colonies were selected and tested by PCR with primers in the sitAB genes (SM100 and SM160) or by plating on chloramphenicol (SM166) to determine the presence or absence of the sit operon.