Biology subjects

Syed, C.

Publications and source records attributed to Syed, C..

2 recordsLinked to original sources

bioRxiv2024

Multiple factors regulate i-motif and G-quadruplex structures in vitro: analysis of repeated and non-repeated polyG/polyC clusters by circular dichroism

The B-form of DNA in the genome contains thousands of sequences that can form various noncanonical structures. Of particular interest are two structures namely G-quadruplex (G4), formed by two or more stacks of four guanine residues in a plane, and intercalating-motif (i-motif, iM) formed by alternately arranged C-C+ pairs. Circular dichroism (CD) spectroscopy is a fast biophysical technique to analyze G4s and iMs. We conducted a CD analysis of two types of DNA sequences, one containing tandem repeats and one without, for the generation of G4s and iMs under various environmental conditions, which include pH, buffer composition, boiling, with flanking sequences, complimentary DNA strands, and single-stranded DNA binding protein (SSB). Changes in pH and boiling caused drastic variations in the CD spectra of DNA containing tandem repeats of GGGGCC and GGCCCC from the C9ORF72 gene, although some changes in G4/iM-forming DNA from promoter-proximal regions of several oncogenes also occur. An increase in the number of hexanucleotide repeats generated complex CD patterns at specific pH due to the presence of both G and C bases. The presence of flanking sequences affects CD pattern of a mixture of G4- and iM-forming sequences of the c-MYC promoter-proximal region. SSB disassembled G4 and iMs of all sequences suggesting an in vivo role for SSBs in disassembly of G4s and iMs during various DNA transactions.

biophysics↗

bioRxiv2023

ExoChew: An exonuclease technique to generate single-stranded DNA libraries

Although DNA in the genome is double-stranded, single-stranded DNA is generated during various processes including DNA replication and repair. Some single-stranded DNAs can form noncanonical structures. Various proteins bind to the single-stranded DNAs site-specifically and/or structure-specifically to regulate various DNA transactions. Because of the transient nature of single-stranded DNAs in the cell, current in vivo techniques may not reveal all such sequences, structures, and protein-DNA complexes. To explore such sequences and structures genome-wide, it is necessary to generate single-stranded DNA libraries. Current in vitro methods involve heat denaturation of libraries of double-stranded DNA fragments followed by cooling to prevent reannealing; however, a significant amount of DNA can reanneal to regenerate double-stranded DNAs. In ExoChew method, double-stranded DNA fragment libraries are enzymatically converted to single-stranded DNA libraries. Genomic DNA is sonicated to generate pools of double-stranded DNA fragments of required size. Each pool of double-stranded DNA fragments is then treated with either T7 exonuclease or E. coli exonuclease III. which recognize and cleave double-stranded DNA from 5 ends or 3 ends, generating single-stranded DNA pools, respectively. The enzymatically generated single-stranded DNA pools can be used for genome-wide studies of protein-DNA interactions and structural studies of DNA.

molecular biology↗