My pLys confusion

philip hardwidge hardp3 at
Mon Apr 1 08:22:43 EST 2002

Check the Novagen catalog.  They have a good summary of the 
different strains and expression plasmids.

If I recall correctly, both pLysS and pLysE encode T7 lysozyme.  This
will inhibit T7 RNAP and thus reduce basal expression.  This is
helpful if one is working with a toxic protein.  Upon addition
of IPTG, repression is relieved, allowing RNAP to become fully activated.
I think pLysE expresses lysozyme more avidly than pLysS.  

Since E. coli is Gram neg, I don't think the effects of the lysozyme 
activity are severe.  However, both pLys plasmids will reduce growth rates 
and tend to reduce total protein yield.  Therefore, use them only when
expression can't be tolerated in BL21(DE3) cells alone.

-Phil Hardwidge

Jeffery Haines (jhaines at wrote:
: Hello all,

: Just wondering if someone can give me the "in a nutshell" summary of 
: pLys.  We're using BL21 cells in the lab I work in, and I've always 
: wondered the purpose of it.  I did the good ol' Google search and I got 
: more confused... 1) encodes T7 lysozyme which inhibits T7 RNA poly (which 
: I guess would be good when you're not expressing protein, but is it still 
: expressed when expression is going on?  (is the lysozyme constantly 
: expressed?).  2)  chops up peptidoglycan in E. coli membr.   
: Is this pLysS thing doing both?  What is pLysE?  Can anyone give me the 
: story or recommend a website that is not trying to advertise a product 
: that is for sale? LOL

: Cheers to all!
: Jeff

: --
: ______________________________________________________________
: Jeff Haines
: 4th year undergrad
: BSc Biochemistry

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