Aawara Chowdhury via (by aawara from
Fri Feb 29 19:25:33 EST 2008

In <u%Uxj.22$TP4.13 from newsfe07.lga>,
 DK <dk from> wrote:

> One thing I am confused about: since its substrate is 
> in the nucleus, you'd expect it to be targeted to nucleus? 
> And yet, the SNAP is a full lenght human cDNA and the 
> company provides a special SNAP plasmid that targets
> the tag to nucleus. How come? Don't all enzymes that 
> work on chromosomes tend to localize to nucleus? 

Those are good observations and questions.  I haven't used the tag,
but here's the information that I had received earlier.  The SNAP tag
is a modified version of 6-O-methylguanine DNA methyltransferase, that
only recognizes para-substituted benzyl guanines.  This substrate is
not recognized by the parental enzyme (and it is claimed, other cellular

The substrate (para-substituted benzyl guanine) is membrane permeable,
so it gets into cells very easily, and by the reaction you described,
modifies the SNAP tag with the para-substituent (which is typically
a fluorophore).

Since nucleotides/nucleosides are both cytoplasmic and nuclear,
presumably the substrate goes to where the SNAP-tagged protein is.

My concern is the same as yours.  Does the tagged protein get dragged 
to the nucleus?

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