Inhibition of human poly(A)-specific ribonuclease (PARN) by purine nucleotides: kinetic analysis

Abstract

Poly(A)-specific ribonuclease (PARN) is a cap-interacting and poly(A)-specific 3′-exoribonuclease that efficiently degrades mRNA poly(A) tails. Based on the enzyme's preference for its natural substrates, we examined the role of purine nucleotides as potent effectors of human PARN activity. We found that all purine nucleotides tested can reduce poly(A) degradation by PARN. Detailed kinetic analysis revealed that RTP nucleotides behave as non-competitive inhibitors while RDP and RMP exhibit competitive inhibition. Mg^{2 +} which is a catalytically important mediator of PARN activity can release inhibition of RTP and RDP but not RMP. Although many strategies have been proposed for the regulation of PARN activity, very little is known about the modulation of PARN activity by small molecule effectors, such as nucleotides. Our data imply that PARN activity can be modulated by purine nucleotides in vitro, providing an additional simple regulatory mechanism.

Keywords::

• PARN
• mRNA
• poly(A) tail
• purine nucleotides
• inhibition

Acknowledgements

We thank Professor Anders Virtanen, Uppsala University (Uppsala, Sweden) for kindly providing us the plasmid for PARN expression and for valuable comments. We also thank Dimitra Levendi, Stamatina Giannouli and Athanasios Kyritsis for support and technical assistance. This work was supported in part by a Research Grant from the University of Thessaly Research Committee.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.