cI gene

[Rafael Maldonado]

On 5 May 1996, ChuCDJK wrote:

> I am trying to find out some information on the cI gene in lamda phages,
> which I believe somehow suppresses the lytic cycle, thereby inducing
> lysogeny.  I was wondering if anyone could confirm this.  Furthermore, I
> have two questions:

I will recomend you the book "Lambda II"; if you cannot find it, the 
lambda regulon can be found in many books of Molecular Genetics as a 
model for prokariotic gene regulation; a good overview is given by "Genes 
IV", by B. Lewin, Oxford University Press (1990), a very common text book 
in Molecular Biology courses.

> 1) What does the cI gene encode, and how does this gene-product suppress
> the lytic cycle?

cI encode a protein; that protein is a repressor, it binds to two regions of 
DNA that are promoters for genes necesary for the cascade of the lytic 
cycle. The binding of cI prevents the binding and action of the RNA 
polymerase. At the same time, cI is an activator of its own gene.
 
> 2) Does the cI gene occur only the lamda genome, or does it also occur on
> the genophores or plasmids of certain host strains?

cI is specific for that binding regions in the lambda DNA, so it is no 
present in other organisms. However, similar "represors" and mode of 
action (binding to DNA sequences to prevent RNA polymerase activity) are 
very common in regulation of genes in prokariotic operons. Other related 
phages have similar proteins, but are called in different ways.


Rafa

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