Guaninreiche

Guaninreiche, in German often used as guaninreiche, describes DNA or RNA sequences that contain a relatively high content of the nucleotide guanine. In genomic contexts this term is especially applied to stretches where guanine bases are abundant and occur in runs that can form stable secondary structures. Such sequences are frequently studied for their potential to adopt noncanonical conformations rather than the standard right-handed double helix.

A key feature of guaninreiche sequences is their ability to form G-quadruplex structures. These are four-stranded assemblies stabilized by Hoogsteen hydrogen bonding between guanine bases, creating guanine tetrads that stack into a G-quadruplex. This folding is favored by certain conditions, notably the presence of potassium ions, and can occur in vitro and, under certain cellular conditions, in vivo. A canonical motif consists of four runs of guanines (G-tracts) separated by short loops, though natural sequences show considerable variation.

Biological significance of guaninreiche regions is an area of active research. G-quadruplex formation in telomeres and gene promoters can influence genome stability, replication, and transcription. In promoter regions of genes such as oncogenes, G-quadruplexes may modulate transcriptional activity, presenting potential targets for therapeutic intervention. Proteins such as specialized helicases help resolve G-quadruplex structures to maintain genome integrity, and small molecules that stabilize G-quadruplexes are being explored for anticancer strategies.

Occurrence and study methods: guaninreiche sequences are widespread in eukaryotic genomes, with notable enrichment near promoters and telomeres. Detection combines bioinformatic motif searches with experimental approaches like circular dichroism, NMR, and chemical probing, as well as the use of G4-specific ligands to investigate their formation and function.