RNA '98 (the RNA Society), Madison, WI

Structure, function, and evolution of RNase P in Archaea.

James W. Brown, Elizabeth S. Haas, James A. Pannucci, Thomas A. Hall, and Daniel Williams.
Department of Microbiology, North Carolina State University

Genes encoding RNase P RNA in 44 species of Archaea have been identified, and the structure of the RNA analyzed by comparative analysis. These RNAs are remarkably similar to their bacterial homologs in both primary and secondary (and presumably tertiary) structure. All of the bacterial consensus structure and nearly all of the invariant nucleotides are also conserved in the archaeal RNAs. It has been surprizing that, unlike their bacterial homologs, the archaeal RNAs were apparently absolutely dependent on protein for function. However, we have recently shown that the RNase P RNAs from two evolutionary lineages of Archaea (the Methanobacteria and extreme halophiles) are catalytically active by themselves in vitro. The extent of activity in these cases is quite small, and requires ionically extreme reaction conditions. The additional components of the archaeal RNase P holoenzyme have yet to be identified; there are no apparent homologs in the available archaeal genome sequences of bacterial, mitochondrial or nuclear RNase P proteins. However, low levels of activity can be reconstituted with some of the archaeal RNase P RNAs and the RNase P protein from the Gram-positive bacterium Bacillus subtilis. The RNase P RNAs from the remaining groups of Archaea are apparently not catalyically active. In the case of the Methanococci and Archaeoglobus, two structural elements (L15 and P8) are missing from these RNAs that, in Bacteria, are critical for substrate binding. The ususual structure of the cruciform (P7-11) in these RNAs has been defined by comparative analysis. The unusual, common structure of this region in Methanococcus and Archaeoglobus implies a phylogenetic relationship between these organisms that is not apparent in trees constructed from ribosomal RNA sequences.