Hi,

I was just given a plasmid for sacB counterselection in mycobacteria. I sequenced this plasmid and I was surprised to find there is a mutation in the signal peptide of the sacB gene.

The person who built this plasmid left long ago, and no one seems to know about this mutation.

Does anyone know if this mutation might be intentional? Or could it be a suppressor mutation from passaging the plasmid in ecoli?

I don't know what to do about this mutation... I could fix it, but this mutation looks like it might be intentional: this mutation precisely breaks cleavage of the signal peptide. As I understand, signal peptide cleavages occurs at the third residue of the motif AXA, this mutation changes the motif to AXV.