Expression and Purification of the CMR (Type III-B) Complex in Sulfolobus solfataricus.

Protein purification is an important technique that allows us to characterize the structural and biochemical properties of either an individual protein or a multi-protein complex. However, expression and purification of one subunit of a complex in the absence of its binding partners has often proven difficult to achieve due to the issues such as instability and mis-folding. This is the case for the components of the CRISPR-Cas interference complexes, which degrade invading nucleic acids in a sequence homology-dependent manner in many prokaryotic species. Here, we describe the expression of a tandem-tagged subunit of the Type III-B (CMR) complex in Sulfolobus solfataricus and subsequent isolation and purification of the whole complex by affinity purification of the tagged subunit.