Regulated Expression of GFP in pGLO
Redrawn from BIO-RAD Biotechnology Explorer Information
Transcriptional Regulation of the Arabinose Operon.
a) In the absence of arabinose: araC blocks transcription of the araB, A and D genes by preventing RNA polymerase binding to the pBAD promoter. B, A and D gene products are not expressed.
araB araA araD pBAD araC arabinose b) In the presence of arabinose: arabinose induces a conformational change in ara C, which allows RNA polymerase to transcribe the araB, A and D genes, which then get translated into enzymes.
araB araA araD pBAD
RNA pol araB araA araD pBAD mRNA pBAD araA araD

Expression of Green Fluorescent Protein in pGLO
In addition to the GFP gene being under the transcriptional control of the pBAD promoter, the Ara C gene is also incorporated into pGLO. This gene is constitutively expressed i.e.
araC protein is always present, thus in the absence of arabinose the GFP gene will not be transcribed and the GFP protein will not be synthesised. In the presence of arabinose the gene will be transcribed, the mRNA will be translated and the protein may be observed by fluorescence under UV light.
GFP pBAD araC arabinose
GFP pBAD
RNA pol
GFP pBAD mRNA pBAD