188 Zero to Genetic Engineering Hero - Chapter 7 - Manually turning on genes in situ
In this chapter, you engineered K12 E. coli with
DNA plasmids with genetic regulation that can be
controlled. While some of the plasmids’ genes were
similar to those used in previous experiments, like
the selection marker genes that automatically turned
on, each of the plasmids had a gene of interest that
was controllable by a different class of environmental
cue - chemical, temperature, and light.
A common theme is that some proteins can either
activate (turn on) or repress (stop) transcription.
A sigma factor that binds to the promoter region
recruits RNA polymerase (or T7 core polymerase) to
cause transcription activation to occur. Conversely,
a protein repressor bound to the operator prevents
transcription until it is removed from the operator.
In fact, during activation, sigma factors (also called
transcription factors) needed to be either created
naturally by the cellular genes, by the genes in the
plasmid you transformed the cell with, or through
chemical modication such as phosphorylation. In
each of these instances, the proteins then bound to
the promoter region to recruit polymerase. During
repression, a protein was ‘roadblocking’ the RNA
polymerase, and an inducer molecule was added
to the cells, which bound to the repressor, changed
its shape, causing it to no longer bind to the DNA
promoter. This allowed RNA polymerase to initiate
You are now well versed in growing cells, genetic engi-
neering, extracting proteins, enzymatic reactions,
and understanding genetic regulations of DNA plas-
mids. Congratulations, Genetic Engineering Hero!
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