Biology Reference
In-Depth Information
CHAPTER
1
Mechanisms of Gene
Regulation: Boolean Network
Models of the Lactose
Operon in
Escherichia coli
Raina Robeva
∗
, Bessie Kirkwood
∗
and Robin Davies
†
∗
Department of Mathematical Sciences, Sweet Briar College, Sweet Briar, VA, USA
†
Department of Biology, Sweet Briar College, Sweet Briar, VA, USA
1.1
INTRODUCTION
Understanding the mechanisms of gene expression is critically important for
understanding the regulation of cellular behavior. Transcription of genes (messen-
ger RNA (mRNA) synthesis), translation of mRNA (protein synthesis), degradation
of mRNA and proteins, and protein-protein interactions are all involved in the con-
trol of gene expression where proteins may bind with DNA, with mRNA, and with
other proteins, leading to complex networks of interactions. Cells have many more
genes than they need to express under any given set of environmental conditions.
Transcription and translation are energetically expensive processes, so cells should
only express the genes required for the environmental circumstances in which they
find themselves.
Certain genes, often termed
housekeeping genes
, are required to support basic
life processes and are expressed continuously. The expression of many other genes,
though, is contingent upon environmental or physiological factors. The expression of
these
regulated genes
is controlled by the cell to ensure efficient use of its energy and
materials. In this chapter we will focus on a set of regulated genes in
Escherichia coli
(
E. coli
), which are expressed only when lactose is the sole sugar available.
The most efficient point for controlling gene expression is at the level of tran-
scription where the cell can control whether or not the gene is transcribed, at what
rate it is transcribed, and under what conditions transcription occurs. Bacteria con-
trol transcription through the binding of specific proteins to their DNA. Some DNA
binding proteins block transcription, while others cause the DNA to bend in a manner
that facilitates the action of RNA polymerase. Still other proteins, the polymerase-
associated sigma factors, confer sequence-specific binding ability on the RNA poly-
merase, allowing it to transcribe genes accurately. In the more complex eukaryotic
cells of higher organisms, multiple proteins may bind to multiple sites in the DNA,
and protein-protein interactions are also involved in the control of transcription.
