Dcp2 Decaps m^2,2,7GpppN-Capped RNAs, and Its Activity Is Sequence and Context Dependent

Abstract

Hydrolysis of the mRNA cap plays a pivotal role in initiating and completing mRNA turnover. In nematodes, mRNA metabolism and cap-interacting proteins must deal with two populations of mRNAs, spliced leader trans-spliced mRNAs with a trimethylguanosine cap and non-trans-spliced mRNAs with a monomethylguanosine cap. We describe here the characterization of nematode Dcp1 and Dcp2 proteins. Dcp1 was inactive in vitro on both free cap and capped RNA and did not significantly enhance Dcp2 activity. Nematode Dcp2 is an RNA-decapping protein that does not bind cap and is not inhibited by cap analogs but is effectively inhibited by competing RNA irrespective of RNA sequence and cap. Nematode Dcp2 activity is influenced by both 5′ end sequence and its context. The trans-spliced leader sequence on mRNAs reduces Dcp2 activity ∼10-fold, suggesting that 5′-to-3′ turnover of trans-spliced RNAs may be regulated. Nematode Dcp2 decaps both m⁷GpppG- and m^2,2,7GpppG-capped RNAs. Surprisingly, both budding yeast and human Dcp2 are also active on m^2,2,7GpppG-capped RNAs. Overall, the data suggest that Dcp2 activity can be influenced by both sequence and context and that Dcp2 may contribute to gene regulation in multiple RNA pathways, including monomethyl- and trimethylguanosine-capped RNAs.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

A dual expression plasmid containing recombinant vaccinia RNA guanylyltransferase and (guanine-N⁷)-methyltransferase was generously provided by Stewart Shuman, human RNA guanylyltransferase by Aaron Shatkin, mRNA cap-specific 2′-O-methyltransferase by Paul Gershon, and cap analogs and nucleotides by Edward Darzynkiewicz. Purified yeast Dcp1/Dcp2 was generously provided by Carolyn Decker and Roy Parker. We thank Jens Lykke-Andersen and members of the Davis lab for their comments on the manuscript.

This work was supported by NIH grant AI49558 and CUNY-CSI startup funds to R.E.D and by NIH grant GM67005 to M.K.