Biology subjects

Guneri, D.

Publications and source records attributed to Guneri, D..

3 recordsLinked to original sources

bioRxiv2023

Prediction of DNA i-Motifs Via Machine Learning

i-Motifs (iMs), are secondary structures formed in cytosine-rich DNA sequences and are involved in multiple functions in the genome. Although putative iM forming sequences are widely distributed in the human genome, the folding status and strength of putative iMs vary dramatically. Much previous research on iM has focused on assessing the iM folding properties using biophysical experiments. However, there are no dedicated computational tools for predicting the folding status and strength of iM structures. Here, we introduce a machine learning pipeline, iM-Seeker, to predict both folding status and structural stability of DNA iMs. The programme iM-Seeker incorporates a Balanced Random Forest classifier trained on genome-wide iMab antibody-based CUT&Tag sequencing data to predict the folding status and an Extreme Gradient Boosting regressor to estimate the folding strength according to both literature biophysical data and our in-house biophysical experiments. iM-Seeker predicts DNA iM folding status with a classification accuracy of 81% and estimates the folding strength with coefficient of determination (R2) of 0.642 on the test set. Model interpretation confirms that the nucleotide composition of the C-rich sequence significantly affects iM stability, with a positive correlation with sequences containing cytosine and thymine and a negative correlation with guanine and adenine. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/571121v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@11f4398org.highwire.dtl.DTLVardef@18eb7e9org.highwire.dtl.DTLVardef@cc49c6org.highwire.dtl.DTLVardef@1ff91a8_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2023

Structural Insights into Regulation of Insulin Expression Involving i-Motif DNA Structures in the Insulin-Linked Polymorphic Region.

The insulin linked polymorphic region (ILPR) is a variable number of tandem repeats (VNTR) region of DNA in the promoter of the insulin gene that regulates transcription of insulin. This region is known to form the alternative DNA structures, i-motifs and G-quadruplexes. Individuals have different sequence variants of VNTR repeats and although previous work investigated the effects of some variants on G-quadruplex formation, there is not a clear picture of the relationship between the sequence diversity, the DNA structures formed, and the functional effects on insulin gene expression. Here we show that different sequence variants of the ILPR form different DNA secondary structures and insulin expression is dependent on formation of i-motif and G-quadruplex structures. The first crystal structure and dynamics of an intramolecular i-motif also reveal sequences within the loop regions forming additional stabilising interactions, which are critical to formation of the stable i-motif structures that modulate insulin expression. The outcomes of this work reveal the detail in formation of stable i-motif DNA structures, with potential for rational based drug design for compounds to alter insulin gene expression.

biophysics↗

bioRxiv2022

The Response of the Eukaryotic Replisome to G-quadruplex- and i-motif-forming Sequences

Sequences that can form DNA secondary structures, such as G-quadruplexes (G4s) and intercalated-Motifs (iMs), are abundant in the human genome and play a range of physiological roles. However, they can also pose a challenge to the replication machinery and in turn threaten genome stability. Multiple lines of evidence suggest G4s interfere with replication, but the underlying mechanism remains unclear. Moreover, there is a lack of evidence of how iMs affect the replisome. Here, we reconstitute replication of physiologically derived structure-forming sequences to find that a single G4 or iM is sufficient to arrest DNA replication. Direct single molecule structure detection within solid-state nanopores reveals structures form as a consequence of replication. A combination of genetic and biophysical characterisation establishes that structure forming capacity is a key determinant of replisome arrest. Mechanistically, replication fork arrest is caused by impaired synthesis, resulting in helicase-polymerase uncoupling. Significantly, iMs also induce breakage of nascent DNA. Finally, stalled forks are only rescued by a specialised helicase, Pif1, but not Sgs1 or Chl1. Altogether, this study provides a potential mechanism for quadruplex structure formation and resolution during replication and highlights G4s and iMs as endogenous sources of replication stress, which may explain their genomic instability and mutation frequencies in cancer.

molecular biology↗