Abstract
Bacterial expression systems are useful tools for protein structure and function analyses. The pET19b vector uses a T7lac
promoter to transcribe target genes using T7 RNA polymerase under control of the lacUV5 promoter in lysogenic Escherichia coli
carrying bacteriophageλ-DE3. Transcription of a target gene is induced by addition of isopropyl-β-d-thiogalactoside (IPTG)
in the medium. However, basal level expression of a target gene occurs under normal culture conditions. This basal level of
protein expression is known to be suppressed by glucose.
In this study, I analyzed the effect of sugars on protein expression in E. coli using the green fluorescence protein gene (gfp). A
pET19b expression vector containing the GFP coding sequence was transformed into the BL21 (DE3) E. coli strain. E. coli
clones expressing gfp were cultured in media supplemented with glucose, galactose, fructose, maltose, sucrose, lactose, or
trehalose for 48 h. During this time, bacterial growth and GFP protein expression were monitored. GFP protein expression
was suppressed by glucose and maltose, but induced by galactose and sucrose. Fructose, lactose, and trehalose initially suppressed
GFP expression, but later induced it.
These data indicate that protein expression is controlled by sugar in the medium. The observed specificities may be due to
differences in sugar transport into the bacteria, regulation of transcription by sugar, and sugar metabolism. These studies suggest
future analyses using inhibitors of sugar transporters and metabolic enzymes.
