Ben F. Luisi coauthored a 2000 X-ray crystallography study of polynucleotide phosphorylase. It revealed a protein trimer with a central channel, providing a structural model for how a multicomponent enzyme might retain and process RNA.[ref]
A duplicated fold is the structural basis for polynucleotide phosphorylase catalytic activity, processivity, and regulation by M. F. Symmons and others. Abstract, Results and Conclusions
The authors' 2002 account supplies the full byline Ben F. Luisi.[ref]The polynucleotide phosphorylase central channel was observed without bound RNA; a role in processivity was proposed rather than directly filmed.[ref]
An original probability model illustrates the proposed retention advantage. Suppose an enzyme completes one cleavage, then remains associated for another with probability , independently after each cleavage. The number of completed cleavages in one encounter hasThus changing from to changes the mean run from to cleavages without specifying how quickly an individual cleavage happens. This invented geometric distribution separates processivity from reaction rate; it is not a fitted model or measured result from Luisi's paper.
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