Abstract
microRNAs (miRNAs) are single-stranded, 21- to 23-nucleotide cellular RNAs that control the expression of cognate target genes. Primary miRNA (pri-miRNA) transcripts are transformed to mature miRNA by the successive actions of two RNase III endonucleases. Drosha converts pri-miRNA transcripts to precursor miRNA (pre-miRNA); Dicer, in turn, converts pre-miRNA to mature miRNA. Here, we show that normal processing of Drosophila pre-miRNAs by Dicer-1 requires the double-stranded RNA-binding domain (dsRBD) protein Loquacious (Loqs), a homolog of human TRBP, a protein first identified as binding the HIV trans-activator RNA (TAR). Efficient miRNA-directed silencing of a reporter transgene, complete repression of white by a dsRNA trigger, and silencing of the endogenous Stellate locus by Suppressor of Stellate, all require Loqs. In loqs f00791 mutant ovaries, germ-line stem cells are not appropriately maintained. Loqs associates with Dcr-1, the Drosophila RNase III enzyme that processes pre-miRNA into mature miRNA. Thus, every known Drosophila RNase-III endonuclease is paired with a dsRBD protein that facilitates its function in small RNA biogenesis.
Highlights
MicroRNAs are 21- to 23-nucleotide singlestranded RNAs that are encoded in the chromosomal DNA and repress cognate mRNA targets [1,2]
A double-stranded RNA-binding domain (dsRBD) Partner Protein for Drosophila Dcr-1 (A) Each of the three D. melanogaster RNase III endonucleases pairs with a different dsRBD protein, which assists in its function in RNA silencing. (B) Differential splicing creates three loqs mRNA variants, loqs RNA splice variant A (RA), RNA splice variant B (RB), and RNA splice variant C (RC). loqs RA and RB are reported in FlyBase
Caenorhabditis elegans, the R2D2-like dsRBD protein RDE-4 is required for RNA interference and interacts with DCR-1, the sole worm Dicer gene [51]
Summary
MicroRNAs (miRNAs) are 21- to 23-nucleotide singlestranded RNAs that are encoded in the chromosomal DNA and repress cognate mRNA targets [1,2]. They are transcribed as long, hairpin-containing precursors [3] by RNA polymerase II [4,5,6,7,8] and processed in the nucleus by the multidomain RNase III endonuclease Drosha [9]. Born as small RNA duplexes, both siRNA and miRNA function in RISC as single-stranded RNA guides for members of the Argonaute family of proteins [26À28]
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