Two-step cleavage of hairpin RNA with 5' overhangs by human DICER
1 RIKEN Omics Science Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
2 Cancer Stem Cell Project, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan
3 Department of Biological Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
4 PREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
BMC Molecular Biology 2011, 12:6 doi:10.1186/1471-2199-12-6Published: 9 February 2011
DICER is an RNase III family endoribonuclease that processes precursor microRNAs (pre-miRNAs) and long double-stranded RNAs, generating microRNA (miRNA) duplexes and short interfering RNA duplexes with 20~23 nucleotides (nts) in length. The typical form of pre-miRNA processed by the Drosha protein is a hairpin RNA with 2-nt 3' overhangs. On the other hand, production of mature miRNA from an endogenous hairpin RNA with 5' overhangs has also been reported, although the mechanism for this process is unknown.
In this study, we show that human recombinant DICER protein (rDICER) processes a hairpin RNA with 5' overhangs in vitro and generates an intermediate duplex with a 29 nt-5' strand and a 23 nt-3' strand, which was eventually cleaved into a canonical miRNA duplex via a two-step cleavage. The previously identified endogenous pre-miRNA with 5' overhangs, pre-mmu-mir-1982 RNA, is also determined to be a substrate of rDICER through the same two-step cleavage.
The two-step cleavage of a hairpin RNA with 5' overhangs shows that DICER releases double-stranded RNAs after the first cleavage and binds them again in the inverse direction for a second cleavage. These findings have implications for how DICER may be able to interact with or process differing precursor structures.