Caps on Eukaryotic mRNAs

Abstract

A 5′‐terminal cap is added to most eukaryotic cellular and viral messenger ribonucleic acids (mRNAs) at an early stage of transcription. Capping is essential and modulates several subsequent events in gene expression including pre‐mRNA splicing, 3′‐poly(A) addition, overall stability, nuclear exit to cytoplasm, protein synthesis, and mRNA turnover initiated by decapping. These and other effects involve cap‐binding proteins that recognise the m7GpppN cap structure. Capping proceeds by a similar series of enzymatic steps in a wide range of systems, but differences exist between metazoans and unicellular eukaryotes and viruses, pointing to capping enzymes as potential targets for the development of selective drugs against some fungal, viral and parasitic infections. Moreover, the unique structural features of caps enable us to define the initiation sites and promoter regions of gene transcription, and provide a basis for advanced sequencer‐mediated high‐throughput genome‐wide profiling of gene expression in a wide range of cell types. Key Concepts: mRNA caps are now known to be essential components of gene expression in eukaryotic organisms. The history of the discovery of the presence of 5′ caps on messenger RNA and its subsequent scientific flowering is a good example of how a seemingly small biochemical observation can lead to the deeper understanding of a wide range of fundamental molecular biological phenomena. Evolution has resulted in wide variations in capping structure and function among organisms ranging from viruses to humans; the selective forces underlying such variation requires more research. Research that has documented viral‐specific capping reactions in viruses should prove to be a fertile source of research leading to new and novel anti‐viral agents. The ‘cap‐snatching’ strategies of influenza viruses is a remarkable example of an apparent adaptation to enhance infectivity and is a particularly compelling target for therapeutic intervention. The NMD mRNA surveillance pathway, which includes a pioneer round of translation with cap‐binding proteins, results in a striking decrease of defective mRNA in cells of patients with genetic diseases containing premature termination codons. Methylation of genomic DNA and mRNA is now widely accepted as a major pathway of the regulation of both transcription and translation in eukaryotes. Protein synthesis is a major field of gene expression where many players work for mRNA capping, decapping, decoding, quality control of gene transcripts and peptide elongation. Micro RNAs are now widely accepted as major players in the translational control of protein synthesis. The analysis of cap‐trapped sequences by high‐throughput sequencers enables one to carry out a genome‐wide identification of promoters together with quantification of their expression, thus elucidating a promoter‐based network of transcriptional regulation.

Refined Young inequality and its application to divergences

“…The results in Theorem 2.5 are mathematical properties on d p (a, b). The inequalities given in (18) gave an improvement of the left hand side in the inequality (7) for the case a, b ≥ 1 and we obtained Theorem 3.7 by (18). We obtained the upper bound of d p (a, b) as a counterpart of (18) for a general a, b > 0.…”

“…However, if there exsits a purpose to find the meaning of the parameter q in divergences based on Tsallis divergence, then we may state that almost theorems (except for Theorem 3.3) hold for 0 ≤ q < 1. In the first author's previous studies [6,7], some results related to Tsallis divergence (relative entropy) are still true for 0 ≤ q < 1, while some results related to Tsallis entropy are still true for q > 1. In this paper, we treated the Tsallis type divergence so it is shown that almost results are true for 0 ≤ q < 1.…”

“…We also give the further bounds on the Jeffreys-Tsallis divergence by the use of Cartwright-Field inequality given in (7). Theorem 3.8.…”

“…Using inequality (7), we deduce q(1 − q) 4 (p j − r j ) 2 p j + max{p j , r j } ≤ d q p j , p j + r j 2 ≤ q(1 − q) 4 (p j − r j ) 2 p j + min{p j , r j } and q(1 − q) 4 (p j − r j ) 2 r j + max{p j , r j } ≤ d q r j , p j + r j 2 ≤ q(1 − q) 4 (p j − r j ) 2 r j + min{p j , r j } .…”