Scientists routinely express heterologous proteins in Escherichia coli. However, these proteins may not fold properly in the bacteria, causing them to aggregate and form insoluble inclusion bodies. Scientists traditionally denature these inclusion bodies with either 8 M urea or 6 M guanidine hydrochloride to solubilize them. These proteins must then be renatured by replacing the denaturants with a gentler buffer. Unfortunately, this process is highly empirical and laborious, and it often results in poor yields. In June 2000, Madison, Wis.-based Novagen Inc. launched the pET 43.1 vector series, specifically to overcome the inclusion body problem. These vectors encode an N-terminal moiety (the Nus·Tag™ sequence) that greatly enhances the solubility of proteins expressed as fusions with the tag. In fact, the polypeptide encoded by the nusA gene (54.8 kDa, 495 amino acids) was carefully selected from more than 4,000 E. coli protein sequences, for having the greatest solubility potential.
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