Fuente: WIPO "tomato" Provided herein is an expression vector comprising a coding nucleic acid sequence encoding a polypeptide of interest, wherein the polypeptide of interest is not constitutively expressed from the vector; and a guide-binding sequence located upstream of the coding sequence, wherein the guide-binding sequence comprises a sequence complementary to a nucleic acid guide; wherein binding of a nucleic acid guide to the guide-binding sequence directs a mutation in a nucleic acid sequence of the vector resulting in expression of the polypeptide of interest. Also provided are a combination comprising the expression vector and a nucleic acid guide, a cell comprising the expression vector and/or nucleic acid guide and associated medical methods and uses.