Polynucleotide phosphorylase binds to ssRNA with same affinity as to ssDNA

Polynucleotide phosphorylase (PNPase, polyribonucleotide nucleotidyltransferase, EC 2.7.7.8) is a multifunctional protein, with a 3'-5' processive exoribonuclease, a Pi exchange, an RNA polymerase and an autoregulatory activity, The interaction between this enzyme and the mRNA target is crucial for its activities. In the present study, we characterized the interaction of PNPase with its mRNA regulatory region and ssRNA, as well as with ssDNA and dsDNA by determining K-d. Our results indicate that PNPase has high affinity for its mRNA, ssRNA and for ssDNA (K(d)similar to10-20 nM). However, this enzyme exhibits a lower affinity for dsDNA (K(d)similar to200-1400 nM). Possible implications of these results on the molecular mechanisms by which PNPase is regulated and degrades mRNA are discussed. (C) 2002 Societe francaise de biochimie et biologie moleculaire/Editions scientifiques et medicales Elsevier SAS, All rights reserved.