definition of "leaky promoter"

Bernard P. Murray, PhD bpmurray*STUFFER* at
Fri Jun 4 20:13:31 EST 1999

In article <pxpst2+-0206992000030001 at>,
pxpst2+ at wrote:

> Am I correct in assuming that the term leaky promoter refers to promoters
> that still drive mRNA production albeit a lower level even when not
> stimulated.

Yes, this is how I understand the term.  It is also dependent
upon promoter context as eg. a glucocorticoid responsive element
can be variably leaky depending on how it is integated into the

> In the eucaryotes, I seem to always see the term used with
> respect to the expression of proteins normally considered to be specific
> to one tissue being expressed in anoother tisse at much lower levels.  Can
> a leaky pomoter also be described as some procaryotic promoter?

It doesn't just refer to tissue "specific" (usually really only selective)
expression but can also refer to controllable promoters such as
GRE or metallothionein in mammalian cells.  There are inducible promoters
that function in bacteria and they can leak (eg. Lac).  There could
also be leaky expression of bacterial genes at inappropriate stages
of growth.  RT-PCR is very sensitive and can pick up low levels of
illegitimate transcription.  Protein expression is often better
controlled than that of RNA but, again, it depends upon your detection
limit.  The most important criterion is if the level of leaky expression
is biologically relevant.

Bernard P. Murray, PhD
Dept. Cell. Mol. Pharmacol., UCSF, San Francisco, USA

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