The original Laemmli system incorporated SDS in the gels and buffers, but SDS is not required in the gel. SDS in the sample buffer is sufficient to saturate proteins, and the SDS in the cathode buffer maintains the SDS saturation during electrophoresis. Precast gels (manufactured gels such as Bio-Rad's Ready Gel®, Mini-PROTEAN®, and Criterion™ Precast Gels) do not include SDS and can be used for either native or SDS-PAGE applications. A range of gel and buffer combinations can be used for native and SDS-PAGE, each with its own advantages (see Electrophoresis Reagent Selection & Preparation for more details).