Gene expression regulation in
prokaryotes
Constitutive versus regulated enzymes
inducible enzymes – catabolic
pathways – complex sugar
metabolism
repressible enzymes – anabolic
pathways (amino acid synthesis)
Regulated expression of enzymes result in
energy savings
Discoveries leading to the operon
model of regulation of gene expression
in bacteria
(lac operon)
• Genes that code for enzymes with related functions tend to be organized in clusters in the chromosome and transcribed as a single unit
• Induction of these protein coding (structural) genes depends on regulatory regions
• Constitutive mutations led to the discovery of two regulatory genes:
lacI – which maps at a distance to the structural genes
lacO – located immediately before the first of the structural genes