I'm reading a paper about CRISPR and they say: "To investigate whether the CasE subunit is sufficient for pre-crRNA cleavage activity, it was overproduced as a fusion with the E. coli maltose binding protein (MalE). Like the complete Cascade, the CasE fusion protein cleaved only the K12-type precrRNA (Fig. 2D), showing that CasE is an unusual endoribonuclease that does not require the other Cascade subunits."
I don't understand why they fuse the CasE to the maltose binding protein of E. coli (MalE). Is it because this MalE is naturally over produced?
Thanks
Hi Carlos, without reference to the paper you are quoting from, it is hard to say for sure. But normally people use maltose fusions to purify proteins from bacteria extracts. I don't know if it is the case in that paper, but it is likely.
Thanks Dmitry. It seems that's the case. This is the reference to the paper:
Brouns, S. J., Jore, M. M., Lundgren, M., Westra, E. R., Slijkhuis, R. J., Snijders, A. P., ... & Van Der Oost, J. (2008). Small CRISPR RNAs guide antiviral defense in prokaryotes. Science, 321(5891), 960-964.
They had to purify the overexpressed protein for use in the cleavage assay (see supplemental materials and methods). Maltose binding protein (MalE) binds to amylose resin, thus purification of the fusion protein is a lot easier than purification of the native protein.
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