The bacterial enzyme polynucleotide phosphorylase (PNPase) is a 3 → S exoribonuclease that degrades mRNA.
(a) The enzyme catalyzes a phosphorolysis reaction, as does glycogen phosphorylase (Section 16-1), rather than hydrolysis. Write an equation for the mRNA phosphorolysis reaction.
(b) In vitro, PNPase also catalyzes the reverse of the phosphorolysis reaction. What does this reaction accomplish and how does it differ from the reaction carried out by RNA polymerase?