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Non-Stop Decay:

It is a cellular procedure of distinguishing and subtracting aberrant transcripts that deficient of a stop codons. These stop codons in the messenger RNA are responsible for instructing the synthesis of proteins to end. The aberrant transcripts are identified meanwhile translation when the ribosome translate into the poly A tail and stop at the 3' end of mRNA. Non-stop transcript can occur when transcriptions revoke owing to point mutation that damage the stop codon. Moreover, some transcriptions are more likely to preserve the low scale of gene expression in a particular state.

The non-stop decay approach discharges the ribosomes that have stalled at the 3' end of mRNA and direct the mRNA to the exosome complex, where it capable of degrading various types of RNA, or to the RNase R in Bacteria.

Liberation of the Ribosome:

The trans-translation procedure is a Bacterial mechanism to solve stalled ribosome at the mRNA. It consists of the hybrid transfer RNA and messenger RNA (tm-RNA) with its important small protein SmpB. When the ribosome stall at the 3'end of mRNA therefor the tm-RNA joined to the bacteria's ribosome from the A site and has amino acid attached to it (11-amino acid tag). Then, the amino acid binds to the polypeptide chain. Then the normal translation will translate the tm-RNA codons sequence that will provide a particular tag which states the incompleteness of the protein. Ultimately, liberated that stalled ribosome.

mRNA Degradation:

Many enzymes and proteins play role in degrading mRNA. For example, in Escherichia Coli there are three enzymes: RNase II, PNPase, and RNase R. RNase R is a 3’-5’ exoribonuclease that recruited to degrade a defective mRNA. RNase R has two distinct structural domains, N-terminal putative helix-turn-helix (HTH) and C-terminal lysine(K-rich) domains. Evidence has been shown the role of K-rich domain in the degradation of non-stop mRNA.These domains are not present in other RNases. Both RNases II and RNase R are members of RNR family, and they have a significant similarity in primary sequence and domain architecture. However, RNase R has unique ability to degrade, while RNase II has less efficient in degrading. Nevertheless, the procedure of degrading mRNA via RNase R has remained anonymous.

References:

Ge, Z., Mehta, P., Richards, J., & Karzai, A. W. (2010). Non‐stop mRNA decay initiates at the ribosome. Molecular Microbiology, 78(5), 1159-1170. doi:10.1111/j.1365-2958.2010.07396.x

Venkataraman, K., Guja, K. E., Garcia-Diaz, M., & Karzai, A. W. (2014). Non-stop mRNA decay: A special attribute of trans-translation mediated ribosome rescue. Frontiers in Microbiology, 5, 93. doi:10.3389/fmicb.2014.00093 Krebs, J. E., Goldstein, E. S., Kilpatrick, S. T., & Lewin, B. (2018). Lewins genes XII. Burlington: Jones & Bartlett Learning.

Alberts, B. M., Johnson, A., & Lewis, J. (2002). Molecular biology of the cell 4th edition. New York: Garland Science.

Klauer, A. A., & Hoof, A. V. (2012). Degradation of mRNAs that lack a stop codon: a decade of nonstop progress. Wiley Interdisciplinary Reviews: RNA, 3(5), 649-660. doi:10.1002/wrna.1124

Hossain, S. T., Malhotra, A., & Deutscher, M. P. (2016). How RNase R Degrades Structured RNA. Journal of Biological Chemistry, 291(15), 7877-7887. doi:10.1074/jbc.m116.717991


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