electrophoretic mobility shift assay PSI-MI MI:0413 band shift This method proves the interaction between a nucleic acid and a protein partner. On the same electrophoresis gel 1 lane is loaded with a nucleic acid of known sequence, a second lane is loaded with the same nucleic acid together with a purified protein (or a protein mixture). The nucleic acid is often radio-labelled to enable visualisation by autoradiography. Comparison of the nucleic acid migration in the two lanes enables the retardation of the nucleic acid due to its interaction with a protein to be observed. emsa Gel retardation assay comigration in gel electrophoresis