Biology Reference
In-Depth Information
Figure 2.10
Gene regulation can be achieved with the use of alternative promoters. A) In this gene,
there are two introns within the coding region. B) The mRNA transcript in larvae uses the promoter
nearest the 5
′
end of the coding region. C) In adults, the promoter further upstream is used and
much of the leader sequence used in larvae is removed by splicing.
longevity of a particular mRNA molecule, 3) regulation of the rate of protein
synthesis, and 4) localization of transcripts where translation is required (
Lipshitz
and Smibert 2000
).
An example of inability to translate an mRNA unless a particular signal is pres-
ent is found in unfertilized eggs, which are biologically static. After fertiliza-
tion, many new proteins are synthesized, including the mitotic apparatus and
cell membranes. However, unfertilized eggs can store large quantities of mRNA
for months or years in an inactive form that abruptly and rapidly become active
within minutes after fertilization. The timing of translation is thus regulated.
2.16 Insulators and Boundaries
Each gene is embedded within a chromosomal environment of other DNA
sequences that have the potential to affect its expression (
Bell et al. 2001, Cai
and Shen 2001
). For example, regulatory elements (enhancers or silencers) asso-
ciated with nearby genes could disrupt normal expression of a gene. To combat
the intrusion of extraneous regulatory elements upon a specific gene, special-
ized DNA sequences called
insulators
provide a barrier against influences from
