Abstract
Ribonuclease P (RNase P) is an essential enzyme required for 5′-maturation of tRNA. While an RNA-free, protein-based form of RNase P exists in eukaryotes, the ribonucleoprotein (RNP) form is found in all domains of life. The catalytic component of the RNP is an RNA known as RNase P RNA (RPR). Eukaryotic RPR genes are typically transcribed by RNA polymerase III (pol III). Here we showed that the RPR gene in Drosophila, which is annotated in the intron of a pol II-transcribed protein-coding gene, lacks signals for transcription by pol III. Using reporter gene constructs that include the RPR-coding intron from Drosophila, we found that the intron contains all the sequences necessary for production of mature RPR but is dependent on the promoter of the recipient gene for expression. We also demonstrated that the intron-coded RPR copurifies with RNase P and is required for its activity. Analysis of RPR genes in various animal genomes revealed a striking divide in the animal kingdom that separates insects and crustaceans into a single group in which RPR genes lack signals for independent transcription and are embedded in different protein-coding genes. Our findings provide evidence for a genetic event that occurred approximately 500 million years ago in the arthropod lineage, which switched the control of the transcription of RPR from pol III to pol II.
Highlights
Ribonuclease P (RNase P) catalyzes the essential removal of the 59 leader sequence from precursor tRNAs [1,2,3,4,5]
The processing of the 59 end of nascent tRNAs is catalyzed by ribonuclease P (RNase P), an essential enzyme
In the ribonucleoprotein form of this enzyme, the RNase P RNA (RPR) functions as a ribozyme aided by protein cofactors
Summary
RNase P catalyzes the essential removal of the 59 leader sequence from precursor tRNAs (pre-tRNAs) [1,2,3,4,5]. Homology among RPPs is restricted to those of archaea and eukaryotes. Biochemical characterization of bacterial RNase P has provided insights into how a single protein cofactor aids RNA catalysis by enhancing affinity for metal ions and substrate recognition [8,9]. Comparisons of bacterial RNase P to its multi-subunit archaeal and eukaryotic counterparts provide an opportunity to examine whether structural and functional attributes of the RPR have been appropriated by additional protein cofactors. Of additional interest is understanding the role of these RPPs in regulating the function of RNase P during development and in response to environmental cues. In our efforts to develop Drosophila RNase P as a multicellular eukaryotic experimental model, we examined the transcription of RPR, and our work has unexpectedly shed some light on the evolution of this ancient ribozyme
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