Transcription RNA editing

The sequence content of some mRNAs is altered after transcription. RNA editing is the term for a change in the base sequence of RNA after transcription by processes other than RNA splicing. RNA editing is prominent in some systems... 

RNA-editing is a posttranscriptional mechanism mediated by RNA editases, which results in a site-selective deamination of adenosine to inosine. This alters codons and splicing in nuclear transcripts and thereby alters the structure and function of proteins. 

Extensive RNA editing of U to C in addition to C to U substitution in the rbcL transcripts of hornwort chloroplasts and the origin of RNA editing in green plants." ... 

Anomalous ubiquitin-B molecules are also present in the brains of control subjects, probably indicating a preneurodegenerative stage. The aberrant proteins show a cellular colocalization compatible with alterations at the transcriptional level or dysfunctional posttranscriptional RNA editing (138). 

Figure 20.20 Summary of transcription, RNA processing and polypeptide synthesis. Polymerisation of the DNA template by RNA polymerase produces pre-mRNA (the primary transcript) this is transcription. The pre-mRNA is now processed, which involves capping, polyadenylation, editing and splicing (see text). The resultant mRNA transfers from the nucleus to the cytosol, where amino acids are polymerised to produce a polypeptide using the instructions present in the codons of the mRNA.

FIGURE 2 RNA editing of the transcript of the cytochrome oxidase subunit II gene from Trypanosoma brucei mitochondria, (a) Insertion of four U residues (pink) produces a revised reading frame, (b) A special class of guide RNAs, complementary to the edited product, may act as templates for the editing process. 

FIGURE 3 RNA editing of the transcript of the gene for the changing a Gin codon to a stop codon and producing a truncated... 

These processes are summarized in Figure 28-1. We have examined several of these mechanisms in previous chapters. Posttranscriptional modification of mRNA, by processes such as alternative splicing patterns (see Fig. 26-19b) or RNA editing (see Box 27-1), can affect which proteins are produced from an mRNA transcript and in what amounts. A variety of nucleotide sequences in an mRNA can affect the rate of its degradation (p. 1020). Many factors affect the rate at which an mRNA is translated into a protein, as well as the posttranslational modification, targeting, and eventual degradation of that protein (Chapter 27). 

Stuart, K., RNA editing in mitochondrial mRNA of trypanoso-matids. Trends Biochem. Sci. 16 68-72, 1991. RNA editing is processing that involves the removal, addition, and modification of nucleotides in the coding regions of nascent transcripts. 

Functionally, in mammalian cells, edited 5-HT2C receptor mRNA isoforms appear to be tissue-specific and function less efficiently than the original non-edited transcript (52,119). Marion et al. (120) reported that RNA edited forms of the 5-HT2C receptor showed lesser degrees of constitutive activity than the... 

The 5 ends of mRNA precursors become capped and methylated in the course of transcription. A 3 poly(A) tail is added to most mRNA precursors after the nascent chain has been cleaved by an endonuclease. RNA editing processes alter the nucleotide sequence of some mRNAs, such as the one for apolipoprotein B. 

A number of oligonucleotide hairpin, quadruplexes and other higher ordered tertiary structures have also been reported the solution structure of the transcriptional antiterminator LicT from Bacillus subtilis bound to a 29 bp ribonucleic antiterminator RNA hairpin " a crystal structure of a kissing complex of the HIV-1 RNA dimerisation initiation site " the crystal structure of the Za high affinity-binding domain of the RNA editing enzyme ADARl bound to left-handed Z-DNA " the crystal structure of parallel quadruplexes from human telomeric DNA. " ... 

Identification of RNA editing sites, chimera transcripts, and RNA-protein interactions RNAa libraries... 

Other modifications of the primary transcript are possible such as alternative splicing which produces mRNAs with different sets of exons and RNA editing in which bases are modified or changed in the original transcript. 

Processing the primary transcript (this includes capping, splicing out introns, addition of the polyA tail, and RNA editing in which specific nucleotides are changed),... 

Fig. 5.6. Quantitative primer extension analysis of RNA editing after RT-PCR. The illustration shows an A to inosine (I) conversion, but the method can be used for any base change. The RT-PCR will convert the inosine to a G. A 32P end-labelled (asterisk) primer is annealed 3 of the edited residue at a distance without any G s between the 3 -end of the primer and the edited site. Extension in the presence of ddCTP, dATP, dTTP and dGTP produces two bands depending on whether the transcript is edited or nonedited.

---