 As the promoter commonly contains binding sequences for proteins affecting transcription, those proteins are also necessary when testing the effects of the promoter.Proteins which associate with the promoter can be identified using an electrophoretic mobility shift assay (EMSA), and the effects of inclusion or exclusion of the proteins with the mutagenized promoters can be assessed in the assay.This allows the use of promoter bashing to not only discover the location on the DNA strand which affects transcription, but also the proteins which affect that strand.