Genetics: From Genes to Genomes

• Isolated a gene that regulates expression of ctx operon• Transformed E. coli containing ctx-lacZconstruct with clonescontaining V. cholerae DNA• Clones that contain a positive regulator should turn on ctx-lacZconstruct.• Identified ToxR, , a transmembrane protein• Identified ToxS, , helps ToxR form dimers which helps it bind to DNA.• What genes does ToxR regulate?• Gene fusions created to constitutive promoter• Fusion introduced into strains of V. cholerae with lacZ randomlyinserted around the genome• Identified intermediate regulator gene ToxT, , a transcriptional activatorthat binds to promoters of many genes, including ctx• ToxR/S or ToxT can activate the ctx genes that produce toxin• ToxT alone activates additional virulence genes which encode piliand other proteins.• Transcription of ToxT is regulated by ToxR/S.Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display17-47