Abstract
Ribonuclease Dicer belongs to the family of RNase III endoribonucleases, the enzymes that specifically hydrolyze phosphodiester bonds found in double-stranded regions of RNAs. Dicer enzymes are mostly known for their essential role in the biogenesis of small regulatory RNAs. A typical Dicer-type RNase consists of a helicase domain, a domain of unknown function (DUF283), a PAZ (Piwi-Argonaute-Zwille) domain, two RNase III domains, and a double-stranded RNA binding domain; however, the domain composition of Dicers varies among species. Dicer and its homologues developed only in eukaryotes; nevertheless, the two enzymatic domains of Dicer, helicase and RNase III, display high sequence similarity to their prokaryotic orthologs. Evolutionary studies indicate that a combination of the helicase and RNase III domains in a single protein is a eukaryotic signature and is supposed to be one of the critical events that triggered the consolidation of the eukaryotic RNA interference. In this review, we provide the genetic insight into the domain organization and structure of Dicer proteins found in vertebrate and invertebrate animals, plants and fungi. We also discuss, in the context of the individual domains, domain deletion variants and partner proteins, a variety of Dicers’ functions not only related to small RNA biogenesis pathways.
Highlights
The gene encoding for Dicer ribonuclease, as reported by Hansen et al [1], was first revealed in 1994 by Bass et al in a screen of the Xenopus ovary cDNA expression library for double-stranded RNA binding proteins [2]
A combination of the Superfamily 2 (SF2) helicase and RNAse III domains in a single protein is considered a eukaryotic signature, and is supposed to be one of the critical, early events that lead to the consolidation of the eukaryotic RNA interference (RNAi) system [44]
In vitro studies revealed that the PAZ domain deletion variants of human Dicer (hDicer) do not process pre-miRNAs and pre-small interfering RNAs (siRNAs); they can cleave single-stranded RNA and DNA substrates, and the resulting products differ in size from typical hDicer products [104]
Summary
The gene encoding for Dicer ribonuclease, as reported by Hansen et al [1], was first revealed in 1994 by Bass et al in a screen of the Xenopus ovary cDNA expression library for double-stranded RNA (dsRNA) binding proteins (dsRBPs) [2]. The CAF gene encoded a putative protein of 1909 amino acids containing an amino (N)-terminal DExH/DEAD-box type RNA helicase domain and a carboxy (C)-terminal RNaseIII-like domain followed by a dsRNA binding domain [6]. In those days, as mentioned above, a highly similar protein of an unknown function was found to be encoded by a fungal and an animal genome, indicating that the CAF-type proteins could play a role in many eukaryotic organisms. They recognize and cleave pre-miRNAs or dsRNAs into functional 21–23-nt miRNAs or siRNAs, respectively In this manuscript, we review the information on the domain organization and structure of Dicer proteins found in vertebrates, with specific emphasizes on hDicer, invertebrates, plants and fungi.
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