Abstract: The present invention relates to a method for optimizing the production of a RNA sequence of interest in a cell, comprising the steps of a) introducing into a plurality of cells a vector capable of expressing a heterologous RNA of interest, wherein said RNA is tagged with a RNA tag comprising an aptamer capable of stabilizing a fluorophore and a scaffold capable of stabilizing the aptamer; b) culturing the cells in a culture medium under conditions that allow expression of the heterologous RNA of interest; c) adding said fluorophore to the culture medium; and d) identifying those cells that show the highest intensity of fluorescence and therefore a high expression of the RNA of interest.

Abstract: The present invention relates to a cell which is genetically modified with respect to its wild type and which comprises a gene sequence coding for a fluorescent protein, wherein the expression of the fluorescent protein depends on the amount of protein that is secreted across the cytoplasmic membrane into the extracytosolic space.

Abstract: The present invention relates to a cell which is genetically modified with respect to its wild type and which comprises a gene sequence coding for a fluorescent protein, wherein the expression of the fluorescent protein depends on the amount of protein that is secreted across the cytoplasmic membrane into the extracytosolic space.