05-07-2012, 01:08 PM
tmRNA Trans-translation
tmRNA & trans-translation(Dhaduk Niketa).ppt (Size: 502 KB / Downloads: 44)
Introduction
It forms a ribonucleoprotein complex together with SmpB,EF-tu & ribosomal protein S1.
In trans-translation,tmRNA and its associated proteins bind to bacterial ribosomes which have stalled in the middle of protein biosynthesis
In the majority of bacteria these functions are carried out by standard one-piece tmRNAs.In other bacterial species,a permuted ssrA gene produces a two-piece tmRNA in which two separate RNA chains are joined by base-pairing
Secondary Structureof tmRNA
It has 5’ and 3’ends of 363 nucleotide
Prominent t-RNA like domain(TLD)
Messanger RNA like domain(MLR)
Four pseudoknots(pk1 to pk4)
RNA helices(no.1 to 12)
One-Piece tmRNAs
Watson-Crick and G-U base pairs were identified by comparing the bacterial tmRNA sequences using automated computational methods in combination with manual alignment procedures.
The base pairing pattern of this prototypical tmRNA, which is organized into 12 phylogenetically supported helices (also called pairings P1 to P12), some divided into helical segments.
TLD - helices 1, 12, and 2a (analogs of the tRNA acceptor stem, T-stem and variable stem, respectively)
MLR-standard tmRNA a large loop containing pseudoknots and a coding sequence (CDS) for the tagpeptide, marked by the resume codon and the stop codon
TRANS-TRANSLATION
A) It postulates that alanine-charged tmRNA recognizes stalled ribosomes.
(B) Binds like a tRNA to the ribosomal A-site,and donates its charged alanine to the nascent polypeptide chain in a standard transpeptidation reaction.
© tmRNA then acts as a surrogate mRNA,replacing the defective mRNA with the self-encoded peptide reading frame.
APPLICATIONS
tmRNA - a novel high-copy-number RNA diagnostic target - its application for Staphylococcus aureus detection using real-time NASBA (Nucleic Acid Sequence Based Amplification).
Features of tmRNA,including its presence in phylogenetically distant bacteria,conserved regions at gene extremities and a potential to serve as target for FISH, make this molecule a possible candidate for identification of bacteria.