Guanine quadruplexes (G4s) serve as regulators of replication, recombination and gene expression. G4 motifs have been recently identified in LTR retrotransposons, but their role in the retrotransposon life-cycle is yet to be understood. Therefore, we inserted G4s into the 3'UTR of Ty1his3-AI retrotransposon and measured the frequency of retrotransposition in yeast strains BY4741, Y00509 (without Pif1 helicase) and with G4-stabilization by N-methyl mesoporphyrin IX (NMM) treatment. We evaluated the impact of G4s on mRNA levels by RT-qPCR and products of reverse transcription by Southern blot analysis. We found that the presence of G4 inhibited Ty1his3-AI retrotransposition. The effect was stronger when G4s were on a transcription template strand which leads to reverse transcription interruption. Both NMM and Pif1p deficiency reduced the retrotransposition irrespective of the presence of a G4 motif in the Ty1his3-AI element. Quantity of mRNA and products of reverse transcription did not fully explain the impact of G4s on Ty1his3-AI retrotransposition indicating that G4s probably affect some other steps of the retrotransposon life-cycle (e.g., translation, VLP formation, integration). Our results suggest that G4 DNA conformation can tune the activity of mobile genetic elements that in turn contribute to shaping the eukaryotic genomes.

• Keywords
• G-quadruplex, N-methyl mesoporphyrin (NMM), Pif1 helicase, Ty1 LTR retrotransposon, retrotransposition, yeast,
• Publication type
• Journal Article MeSH

p53 is one of the most studied tumor suppressor proteins that plays an important role in basic biological processes including cell cycle, DNA damage response, apoptosis, and senescence. The human TP53 gene contains alternative promoters that produce N-terminally truncated proteins and can produce several isoforms due to alternative splicing. p53 function is realized by binding to a specific DNA response element (RE), resulting in the transactivation of target genes. Here, we evaluated the influence of quadruplex DNA structure on the transactivation potential of full-length and N-terminal truncated p53α isoforms in a panel of S. cerevisiae luciferase reporter strains. Our results show that a G-quadruplex prone sequence is not sufficient for transcription activation by p53α isoforms, but the presence of this feature in proximity to a p53 RE leads to a significant reduction of transcriptional activity and changes the dynamics between co-expressed p53α isoforms.

• Keywords
• p53 protein, protein-DNA interaction, transactivation potential,
• MeSH
• G-Quadruplexes * MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 genetics   metabolism   MeSH
• Promoter Regions, Genetic genetics   MeSH
• Protein Isoforms genetics   metabolism   MeSH
• Apoptosis Regulatory Proteins genetics   metabolism   MeSH
• Proto-Oncogene Proteins genetics   metabolism   MeSH
• Response Elements genetics   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• BBC3 protein, human MeSH Browser
• Tumor Suppressor Protein p53 MeSH
• Protein Isoforms MeSH
• Apoptosis Regulatory Proteins MeSH
• Proto-Oncogene Proteins MeSH