STRUCTURE OF THE DSRNA BINDING DOMAIN OF ESCHERICHIA-COLI RNASE-III

The double-stranded RNA binding domain (dsRBD) is a similar to 70 resi due motif found in a variety of modular proteins exhibiting diverse fu nctions, yet always in assocation with dsRNA. We report here the struc ture of the dsRBD from RNase III, an enzyme present in most, perhaps a ll, living cells. It is involved in processing transcripts, such as rR NA precursors, by cleavage at short hairpin sequences. The RNase III p rotein consists of two modules, a similar to 150 residue N-terminal ca talytic domain and a similar to 70 residue C-terminal recognition modu le, homologous with other dsRBDs. The structure of the dsRBD expressed in Escherichia coli has been investigated by homonuclear NMR techniqu es and solved with the aid of a novel calculation strategy. It was fou nd to have an alpha-beta-beta-beta-alpha topology in which a three-str anded anti-parallel beta-sheet packs on one side against the two helic es. Examination of 44 aligned dsRBD sequences reveals several conserve d, positively charged residues. These residues map to the N-terminus o f the second helix and a nearby loop, leading to a model for the possi ble contacts between the domain and dsRNA.