Drosophila RNase H1 is essential for development but not for proliferation

Ribonucleases H (RNases H) recognize and specifically degrade RNA that is b ound to complementary DNA and are thought to be involved in DNA replication and transcriptional regulation. Though it was previously shown that bacter ial RNases H participate in DNA synthesis, none of the known mutations in R Nase H genes in either prokaryotes or lower eukaryotes is lethal. Here, we report the characterization of the first loss-of-function mutation in an RN ase Hl gene in a metazoan organism, Drosophila melanogaster. Genetic studie s of this mutant showed that this gene is essential for metamorphosis in Dr osophila. However, disruption of the RNase HI gene does not affect prolifer ation, but probably alters the regulation of gene expression. The lethal ph enotype of this mutant also demonstrates that RNase HI activity in Drosophi la cannot be provided by other cellular RNase H activities. Analysis of the developmental and spatial expression profiles of a reporter gene placed un der the control of the RNase HI promoter revealed increased expression in s everal larval tissues. In salivary glands this increase was shown to be ind ucible by treatment with ecdysone.