A novel type of RNase III family proteins in eukaryotes

The RNase III family of double-stranded RNA-specific endonucleases is chara cterized by the presence of a highly conserved 9 amino acid stretch in thei r catalytic center known as the RNase III signature motif. We isolated the drosha gene, a new member of this family in Drosophila melanogaster. Charac terization of this gene revealed the presence of two RNase III signature mo tifs in its sequence that map indicate that it is capable of forming an act ive catalytic center as a monomer. The drosha protein also contains an 825 amino acid N-terminus with an unknown function; A search for the known homo logues of the drosha protein revealed that it has a similarity to two adjac ent annotated genes identified during C. elegans genome sequencing. Analysi s of the genomic region of these genes by the Fgenesh program and sequencin g of the EST cDNA clone derived from it revealed that this region encodes o nly one gene. This newly identified gene in nematode genome shares a high s imilarity to Drosophila drosha throughout its entire protein sequence. A po tential drosha homologue is also found among the deposited human cDNA seque nces. A comparison of these drosha proteins to other members of the RNase I II family indicates that they form a new group of proteins within this fami ly. (C) 2000 Published by Elsevier Science B.V. All rights reserved.