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How do I determine the apparent molecular weight of a protein?

Some proteins migrate anomalously on SDS gels; therefore the molecular weight estimate obtained is referred to as the apparent molecular weight. When determining the apparent molecular weight of a protein, do not compare your protein of interest to prestained protein molecular weight markers. Prestained molecular weight markers will run differently than unstained proteins; use unstained protein molecular weight markers and stain the gel after electrophoresis.

LabFact #35

When expressing your protein in a cell-free system, make sure the combination of promoter and DNA conformation is appropriate. For example, the T7 RNA polymerase promoter may express better in a linearized template while the SP6 promoter transcribes better in a circular DNA.

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