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Instability within the coding sequence of the repetitive RNA polymerase II C‐terminal domain
Author(s) -
Exner Alexandra E,
Fuchs Stephen M
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.793.5
Subject(s) - ctd , biology , trinucleotide repeat expansion , genetics , coding region , dna , repeated sequence , rna polymerase ii , gene , microbiology and biotechnology , genome , gene expression , promoter , allele , oceanography , geology
The carboxyl‐terminal domain (CTD) of RNA polymerase II is composed of a conserved tandemly repeating 7 amino acid sequence and plays an essential role in transcription. We and others have shown that number of CTD repeats differs between species (e.g. 26 in yeast, 52 in humans) but also, variability is seen amongst individuals within a single species. The DNA that encodes repetitive amino acid sequences is thought to be unstable and prone to both expansion and contraction of the DNA sequence, resulting in protein products of different length. Previous studies have shown mutations that confer a shorter CTD protein product impair growth and spontaneous suppressor mutations can arise in which the CTD coding region rearranges by either expansion or contraction to improve growth. Our goal was to study this plasticity of the CTD by measuring the rate at which the CTD contracted to repair a series of premature stop codons. Specifically, we inserted stop codons after repeats 8–11, which produced a shortened protein product and lead to decreased growth. The CTD was indeed able to contract and delete the stop codon‐containing repeats, and often delete extra repeats in the contraction process. To explore the mechanisms involved in these contraction events, we measured mutation frequency in yeast in which factors important for DNA repair had been deleted. Our results show that, unlike CTD expansion, which requires homologous recombination, contraction percentage was greatly increased in rad52 Δ cells. We have used this data to build a CTD contraction model wherein we propose that the DNA encoding the repetitive CTD region is unstable, and nonessential repeats act as a template during DNA repair to confer plasticity. These findings will be helpful in explaining the variation in CTD repeat number amongst individuals within a species, as well as a useful general model for the instability in genomic regions encoding repetitive amino acid sequences. Support or Funding Information Start up funding from Tufts University