BIRTH OF THE SNORNPS - THE EVOLUTION OF RNASE MRP AND THE EUKARYOTIC PRE-RIBOSOMAL-RNA-PROCESSING SYSTEM

The ribonucleoprotein particle RNase MRP is required for the processin g of yeast pre-ribosomal RNA (pre-rRNA). A structurally related partic le, RNase P, is universally required for processing of pre-tRNA, but i n bacteria and archaea also cleaves a site in the pre-rRNA. This sugge sts that RNase MRP may have arisen in eukaryotes as a form of RNase P specialized for pre-rRNA processing. Other eukaryotic small nucleolar RNAs may have arisen as trans-acting factors that functionally replace cis-acting pre rRNA interactions in bacteria and archaea.