Functional Evolution in Orthologous Cell-encoded RNA-dependent RNA Polymerases
Hamid, Fursham M.
El Sahili, Abbas
Darwis, Dina Amallia
Wong, Yee Hwa
Makeyev, Eugene V.
Date of Issue2016
School of Biological Sciences
Many eukaryotic organisms encode more than one RNA-dependent RNA polymerase (RdRP) that likely emerged as a result of gene duplication. Such RdRP paralogs often participate in distinct RNA silencing pathways and show characteristic repertoires of enzymatic activities in vitro. However, to what extent members of individual paralogous groups can undergo functional changes during speciation remains an open question. We show that orthologs of QDE-1, an RdRP component of the quelling pathway in Neurospora crassa, have rapidly diverged in evolution at the amino acid sequence level. Analyses of purified QDE-1 polymerases from N. crassa (QDE-1Ncr) and related fungi, Thielavia terrestris (QDE-1Tte) and Myceliophthora thermophila (QDE-1Mth), show that all three enzymes can synthesize RNA but the precise modes of their action differ considerably. Unlike their QDE-1Ncr counterpart favoring processive RNA synthesis, QDE-1Tte and QDE-1Mth produce predominantly short RNA copies via primer-independent initiation. Surprisingly, a 3.19 Å-resolution crystal structure of QDE-1Tte reveals a quasi-symmetric dimer similar to QDE-1Ncr. Further electron microscopy analyses confirm that QDE-1Tte occurs as a dimer in solution and retains this status upon interaction with a template. We conclude that divergence of orthologous RdRPs can result in functional innovation while retaining overall protein fold and quaternary structure.
RNA-dependent RNA polymerase
Journal of Biological Chemistry
© 2016 The American Society for Biochemistry and Molecular Biology. This is the author created version of a work that has been peer reviewed and accepted for publication by Journal of Biological Chemistry, The American Society for Biochemistry and Molecular Biology. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1074/jbc.M115.685933].