Journal club: Lee .. Ha, Science 2013

Jeff Moffitt

Elastic coupling between RNA degradation and Unwinding by Exoribronuclease (Lee … Ha, Science 2013)

• Exosome at core of RNA modification / degradation in yeast.
• complex conserved through domains of life. called PNPase in bacteria
• some core elements of bacterial complex are catalytically inactive in bacteria, and replaced by the catalytic component studied in this paper.
• long lived intermediates in degredation — discrete unwinding steps. fundamental step size is ~4 nt (def. greater than 1, despite single basepair degradation).
• exponentially distributed step size despite 4 bp hydrolysis, suggests some other event is rate limiting.
• Model: chew forward 4 bases, compression pushes forward unzipping, unzips 4 bases, chews forward the next 4. Elastic energy may be in stretching the RNA or in compressing the protein ‘spring’ linker.
• unwinding and digestion movement are decoupled. *NaCl increases duplex stability.