Functional characterization of RNase H1 from Drosophila melanogaster.

We have cloned and functionally characterized the RNase H1 gene from D. melanogaster. The longest open reading frame consists of 5 exons that encode a 333 amino acid protein with a molecular mass of 37.1 kDa. This is the first demonstration of specific nuclease activity of a cloned RNase gene from a multicellular higher eukaryote. No additional proteins or cofactors are required for this nuclease activity. Comparison of Drosophila RNase H1 amino acid sequence to that of other cellular eukaryotic homologs reveals the presence of three evolutionarily distinct domains. The N- and C-terminal conserved domains are connected by a highly variable domain. The C-terminal domain has high amino acid similarity to bacterial RNase HI and the RNase H domain of retroviral reverse transcriptase, while the N-terminus, of unknown function, is similar to the P6 translational activator of caulimoviruses.