A +1 frameshifting

Frameshift suppression is also possible. This can be achieved by a second mutation in a tRNA gene such that the anticodon of a tRNA molecule consists of 4 bases rather than 3, for example, an extra C residue in the CCC anticodon sequence of a glycine tRNA gene. This change will allow correction of a +1 frameshift involving the GGG codon for glycine (Bossi, 1985). 

Mutagenesis studies showed that this type of mutation induced a -1 frameshift. A further report describes the incorporation of an (adjacent) cis-syn cyclobutane dimer site specifically into a nucleosome The templating properties of the thymine photoproducts, including the Dewar photoproduct (176), have been examined using the pyrene C-nucleoside triphosphate. The pyrene nucleotide was inserted in preference to dATP opposite the 3 -T of the photoproducts in all cases except for a trans,syn photoproduct, whereas dATP was preferentially incorporated opposite the 5 -T in all cases. This suggests that the incorporation opposite the 3 -end of the photoproduct takes place via a transient abasic site-like intermediate. 

Utilising a reversion assay in Salmonella enterica, Prieto et al reported an increased frequency of point mutations following bile-salt exposure. Mutations were predominantly nucleotide substitutions (GC to AT transitions) and -1 frameshift mutations.The frameshifts were dependent on SOS induction and linked to the activity of DinB polymerase (Pol IV). The authors proposed that the GC to AT transitions stimulated by bile, could have arisen from oxidative processes giving rise to oxidised cytosine residues. Consistent with this hypothesis, the authors demonstrated that strains of S. enterica-lacking enzymes required for base-excision repair (endonuclease III and exonuclease IV) and the removal of oxidised bases, demonstrated increased bile-acid sensitivity compared with competent strains. In another study using E. coli, resistance to the DNA-damaging effects of bile was associated with Dam-directed mismatch repair, a pathway also involved with the repair of oxidative DNA lesions. ... 

McNaugton, B. R. Gareiss, P. C. Miller, B. L. Identification of a selective small-molecule ligand for HIV-1 frameshift-inducing stem-loop RNA from an 11,325 member resin bound dynamic combinatorial library. J. Am. Chem. Soc. 2007, 129(37), 11306-11307. 

Lee SI, Umen JG, Varmus HE (1995) A genetic screen identifies cellular factors involved in retroviral-1 frameshifting. Proc Natl Acad Sci USA 92 6587-6591 Leeds P, Peltz SW, Jacobson A, Culbertson MR (1991) The product of the yeast UPFl gene is required for rapid turnover of mRNAs containing a premature translational termination codon. Genes Dev 5 2303—... 

The product of the pol gene (reverse transcriptase) is translated as a larger polyprotein, on the same mRNA that is used for the gag protein alone (see Fig. 26-30). The polyprotein, or gag-pol protein, is then trimmed to the mature reverse transcriptase by proteolytic digestion. Production of the polyprotein requires a translational frameshift in the overlap region to allow the ribosome to bypass the UAG termination codon at the end of the gag gene (shaded pink in Fig. 1). 

Some mRNA sequences have been found that cause low-to-moderate frameshifts without the aid of nearby stimulator sequences. These sequences include the four consecutive U residues at the 3 end of T7 gene 10, which permit a 10% frameshift into the - -1 frame to yield protein lOB (14) and the sequence CCC UGA, which permits a 3% - -1 frameshift... 

Translational frameshifting. Certain mRNAs appear to contain structural information that, if activated, results in a +1 or -1 change in reading frame. This translational frameshifting, which has been most often observed in cells infected by retroviruses, allows more than one polypeptide to be synthesized from a single mRNA. 

Pol IV replicates undamaged DNA only around 5-fold less accurately than the catalytic a-subunit of Pol III [76]. It is prone to making -1 frameshift mutations in homopolymeric runs of six or more GC base pairs base substitutions also result (18-30%) [71, 90]. However, Pol IV s most striking quality is its ability to accurately... 

The y subunit is encoded by a portion of the gene for the r subunit, such that the amino-terminal 66% of the t subunit has the same amino acid sequence as the y subunit. The y subunit is generated by a translational frameshifting mechanism (see Box 27-1) that leads to premature translational termination. 

Bartram, C, Edwards, R. H. T., Clague, J., and Beynon, R. J. (1994). McArdle s disease A rare frameshift mutation in exon 1 of the muscle glycogen phosphorylase gene. Biochim. Biophys. Acta 1226, 341-343. 

This complexity is particularly well illustrated by the bypass of a site-specific B [ d P-guanine adducts in E. coli. Within the GGA sequence context (the adducted base shown in bold), both error-free and —1 frameshift bypass pathways depend on both Pol IV and Pol V, whereas the G to T... 

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