Solution structure of the Drosha double-stranded RNA-binding domain

We report here the solution structure of the dsRBD from Drosha (Drosha-dsRBD). The αβββα fold is similar to other dsRBD structures. A unique extended loop distinguishes this domain from other dsRBDs of known structure.Despite uncertainties about RNA-binding properties of the Drosha-dsRBD, its structure suggests it retains RNA-binding features. We propose that this domain may contribute to substrate recognition in the Drosha-DGCR8 Microprocessor complex.MicroRNA (miRNA) are small regulatory RNAs derived from longer RNA transcripts called primary miRNA (pri-miRNA) ([1], reviewed recently in [2]). Pri-miRNA are cleaved by an RNase III family enzyme called Drosha to produce hairpin precursor miRNA (pre-miRNA) [3]. Pre-miRNA are transported to the cytoplasm [4-7] and further processed by Dicer enzymes to produce mature miRNA [8-13]. Drosha contains two RNase III domains that form the enzyme's catalytic center. At the C-terminus is a double-stranded RNA-binding domain (dsRBD), which is essential for pri-miRNA processing [14].To process pri-miRNA, Drosha forms an enzyme complex with a partner protein DiGeorge syndrome critical region 8 (DGCR8; also known as Pasha in Drosophila and Caenorhabditis elegans) [14-17], which contains two dsRBDs. DGCR8 has been proposed to be a crucial factor for recognition of pri-miRNA substrate via its dsRBDs [18]. A crystal structure of the tandem dsRBDs of DGCR8 revealed closely interacting domains whose conformation would not be expected to change upon RNA binding [19]. A model for RNA recognition suggests that the two domains bind to portions of the pri-miRNA that are distant from each other. It is not known whether the dsRBD of Drosha is also important for substrate RNA binding or serves another function, since little to no RNA-binding activity has been observed for Drosha and the dsRBD is not necessary for interaction with DGCR8 [14,18,20,21]. To gain insight into the function of Drosha-dsRBD, we determined the solution structure of this