Probing Gene Expression in Live Cells, One Protein Molecule at a Time

TLDR

The authors directly visualized real‑time synthesis of individual protein molecules in *E. coli* by expressing a fast‑maturing YFP fusion targeted to the membrane, enabling single‑molecule detection under repressed conditions.

Abstract

We directly observed real-time production of single protein molecules in individual Escherichia coli cells. A fusion protein of a fast-maturing yellow fluorescent protein (YFP) and a membrane-targeting peptide was expressed under a repressed condition. The membrane-localized YFP can be detected with single-molecule sensitivity. We found that the protein molecules are produced in bursts, with each burst originating from a stochastically transcribed single messenger RNA molecule, and that protein copy numbers in the bursts follow a geometric distribution. The quantitative study of low-level gene expression demonstrates the potential of single-molecule experiments in elucidating the workings of fundamental biological processes in living cells.