Table 1

Specificity of CTXφ RstR repressors for rstA promoters

ReporterRstR repressor*
Classical (pHK2) El Tor (pHK1) V. cholerae CTXφ lysogen
−Arabinose+Arabinose−Arabinose+ArabinoseClassicalEl Tor
Classical rstA-lacZ (pHK 101)5277688933574
El Tor rstA-lacZ (pHK102)1571672551.22601
  • β-Galactosidase units are reported as nmol of o-nitrophenyl β-d-galactoside hydrolyzed per min per OD600. Assays were performed in triplicate, and the average value is presented. 

  • * The arabinose-inducible classical (pHK2) or El Tor (pHK1) rstR plasmids were introduced along with an rstA-lacZ reporter plasmid into Escherichia coli strain CC118 (21). Cultures were grown in L broth (25) for 16 hr in the presence or absence of 0.05% arabinose, and the β-galactosidase activity was determined (25). 

  • The classical and El Tor rstA-lacZ reporters were introduced into lacZ derivatives of classical (0395) and El Tor (E7946) V. cholerae CTXφ lysogens, and the activity of β-galactosidase was determined (25).