Molecular Biology of the Gene 7th Edition by Richard Losick, James Watson, Michael Levine, Tamara Baker, Alexander Gann

Exercise 11

You find a complex composed of a protein moiety and an RNA moiety that is capable of cleaving an RNA substrate. You want to know which moiety is responsible for catalysis. You perform an in vitro cleavage assay in the proper buffer conditions containing a low concentration of Mg 2+. The table below summarizes the results from performing seven separate reactions. The + symbol indicates the included reaction components. Sper-midine is a positively charged peptide not specific to this reaction.

A. Does the protein or RNA moiety act as the catalyst in this reaction? Explain which reactions helped you make your conclusion.
B. Propose the function of spermidine in the last two reactions.