III. Complex Stability
Two DGCR8 subunits directly bind to DROSHA through
interaction between a helix and an RIIID subunit,
respectively. The two DGCR8 binding sites are asymmetric on
the the RIIID subunits; DGCR8 binds RIIIDa on helices 3,4,
and 9, while it binds RIIIDb on helices 1,5, and 8 (not
shown). The RIIIDb-CTT (of DGCR8) interaction is more
important than that with RIIIDa for microprocessor complex
stability and formation. Two surprising
may play an important role in stability by bridging
different structural modules.
Cys536, Cys536, and
His680, Cys676, and
IV. Pre-miRNA Processing
Unlike the well-described DICER system, it is not
entirely clear how DROSHA functions to process miRNAs.
However, some predictions may be made based on a model
of DROSHA-RNA binding. A prior model of two subunits
with a manufactured RNA
substrate shows orientation within the complex.
Within the DROSHA complex, the apical loop of the dsRNA
segment orients towards the RNase III domains, with the
basal segments of the RNA positioned towards the center
domain (CED) of the protein. The
( RIIIDa and
RIIIDb ) of the RNase domains indicate that RIIIDa
cleaves the 3’ strand of the RNA while RIIIDb cleaves the 5’
of the RNase domain is positioned next to the last
base pair of the dsRNA region.
, specifically, is highly conserved and its mutation inhibits cleavage
activity. It is possible that the bump helix allows DROSHA
to function as a “ruler,” measuring out 11 base pairs from
the last base pair before cleavage.
Davidson, Beverly L. and Paul B. McCray.
2011. Current Prospects for RNA Interference -Based
Therapies. Nature Reviews Genetics. 12:329-340.
Gan, Jianhua, Joseph E. Tropea,
Brian P. Austin, Donald L. Court, David S. Waugh, and
Xinhua Ji. 2006. Structural Insight into the Mechanism of
Double-Stranded RNA Processing by Ribonuclease III. Cell.
Kwon, S. Chul, Tuan Anh Nguyen,
Yeon-Gil Choi, Myung Hyun Jo, Sungchil Hohng, V. Narry
Kim, and Jae-Sung Woo. 2015. Structure of Human DROSHA. Cell.
Nguyen, Tuan Anh, Myung Hyun Jo,
Yeon-Gil Chol, Joha Park, S. Chil Kwon, Sungchul Hohng, V.
Narry Kim, and Jae-Sung Woo. 2015. Functional Anatomy of
Human Microprocessor. Cell. 161:1374-1387.
Watson, James D., Tania A. Baker,
Stephen P. Bell, Alexander Gann, Michael Levine, Richard
Losick, with Stephen C. Harrison. 2014. Molecular Biology
of the Gene. Cold Spring Harbor Laboratory Press.
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