Everything about Rnase P totally explained
Ribonuclease P (RNase P) is a type of
Ribonuclease that's currently under heavy research. RNase P is unique from other
RNases in that it's a
ribozyme – a
ribonucleic acid that acts as a catalyst in the same way that a
protein based enzyme would. Its function is to cleave off an extra, or precursor, sequence of RNA on
tRNA molecules . Further RNase P is one of two known multiple turnover ribozymes in nature (the other being the
ribosome), the discovery of which earned Professor
Sidney Altman the
Nobel Prize in Chemistry in 1989. In fact, Sidney Altman discovered the existence of
precursor tRNA with flanking sequences and was the first to characterize RNase P and its activity in processing of the 5' leader sequence of precursor tRNA back in the 70's. Recent findings also reveal that RNase P has a new function . It has been shown that human nuclear RNase P is required for the normal and efficient transcription of various
small noncoding RNA genes, such as tRNA,
5S rRNA,
SRP RNA and
U6 snRNA genes, which are transcribed by
RNA polymerase III, one of three major nuclear RNA polymerases in human cells.
In bacteria
In
bacteria, such as
E. coli, RNase P has two components: an RNA chain, called M1 RNA, and a polypeptide chain, or protein, called C5 protein, .
In vivo, both components are necessary for the ribozyme to function properly, but
in vitro, the M1 RNA can act alone as a catalyst . The primary role of the C5 protein is to enhance the substrate binding affinity and the catalytic rate of the M1 RNA enzyme probably by increasing the metal ion affinity in the active site. The crystal structure of bacterial RNase P RNA has been recently resolved, revealing its flat surface that's generated by a number of coaxially stacked helical domains connected by local and long-range contacts. This flat surface facilitates binding and cleavage of precursor tRNA substrates. For review see .
In archaea
In
archaea, RNase P
ribonucleoproteins consist of 4-5 protein subunits that are associated with RNA. As revealed by in vitro reconstitution experiments these protein subunits are individually dispensable for tRNA processing that's essentially mediated by the RNA component,, . The structures of protein subunits of archaeal RNase P have been resolved by
x-ray crystallography and
NMR, thus revealing new protein domains and folding fundamental for function.
It has recently been argued that the archaebacteriium
Nanoarchaeum equitans doesn't possess RNase P. Computational and experimental studies failed to find evidence for its existence. In this organism the tRNA promoter is close to the tRNA gene and it's thought that transcription starts at the first base of the tRNA thus removing the requirement for RNase P.
In eukaryotes
In
eukaryotes, such as humans and
yeast, RNase P consists of an RNA chain that's structurally similar to that found in bacteria as well as nine to ten associated proteins (as opposed to the single bacterial RNase P protein, C5), . Five of these protein subunits exhibit homology to archaeal counterparts. These protein subunits of RNase P are shared with
RNase MRP,,, a catalytic ribonucleoprotein involved in processing of ribosomal RNA in the
nucleolus . RNase P RNA from eukaryotes was only recently demonstrated to be a ribozyme . Accordingly, the numerous protein subunits of eucaryal RNase P have a minor contribution to tRNA processing per se, while they seem to be essential for the function of RNase P and RNase MRP in other biological settings, such as gene transcription and the
cell cycle, .
Further Information
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