Artifacts in sodium dodecyl sulfate-polyacrylamide gel electrophoresis due to 2-mercaptoethanol

Mercaptoethanol, when present in the sample buffer during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is responsible for the appearance of two nonprotein bands (electrophoretic mobilities corresponding to 68 and 54 kdalton) stainable with silver and with Coomassie blue. After iodination in vitro of DNA preparations isolated by alkaline phenol extraction using chloramine-T procedure, part of the radioactive label is found in these bands, provided the reaction is terminated by mercaptoethanol, whereas only a diffuse background is present in this area if the reaction is stopped by sodium metabisulfite. Similar results are obtained with highly purified total cytoplasmic RNA. The results indicate that the appearance of the 68- and 54-kdalton bands is in artifact. The relevance of these results to the proteins tightly bound to DNA is discussed.