M13: plates are all blue!

[Mikhail Alexeyev]

In article <JO_C.6.30463E2D at vcp.monash.edu.au>, JO_C at vcp.monash.edu.au (Jo
Caine) wrote:

> Hi,
> 
> I've just done a M13 transformation and plated out in top agar the lawn
cells, 
> IPTG, X-gal and the transfored cells.  This morning all the plates are a 
> lovely shade of blue.  The lawn is intact and there are some plaques, but I 
> can't tell the color of them because of the blue background.  
> Has anyone got any explaination?  The same transformation worked last week.  
> Could one of the reagants gone off in that time?

You could've gotten a blue lawn if you used by mistake lac+ bacteria, say,
HB101, K802, LE392, etc. (lacY1 mutation does not prevent blue
coloration). If these bacteria (that is often a case) do not have F prime,
they will not give rize to plaques. Just my 2 cents...

Misha.