Abstract

Publisher Summary It has been demonstrated that 5′ → 3′-ribonucleases play an important role in the decay of mRNAs in yeast cells. A 5′ → 3′-ribonuclease from yeast cells named Xrn1p has been purified and cloned. Other 5′ → 3′-exoribonucleases have been partially purified from nuclei of mammalian cells. Coutts and Brawerman found that extracts of mouse sarcoma 180 cells possess a 5′ → 3′-exoribonuclease that can cleave both capped and uncapped mRNA. They observed that the initial cleavage of the substrate could occur at either the first, second, or probably the third phosphodiester linkage in some RNAs. The purification and characterization of a 5′→ 3′-exoribonuclease from rabbit reticulocytes that degrades capped and uncapped RNAs has been reported. This chapter summarizes information about the reticulocyte enzyme. The exoribonuclease appeared to be reasonably stable when stored at -70°C. No significant loss in activity was observed over a 3-month period. The enzyme was heat labile. Incubation for 10 min at 45°C led to loss of about 90%of activity. The purified enzyme possessed a normal ultraviolet spectrum and appeared to be free of nucleic acids or nucleotides.

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