ATrich

ATrich is a term used in genetics and genomics to denote regions of DNA that have a high proportion of adenine and thymine nucleotides. In discussions of genome composition, AT-rich regions are typically contrasted with GC-rich regions, with the degree of richness defined by specific thresholds that can vary by study or species.

Characteristics of AT-rich regions include lower thermal stability due to weaker A–T base pairing, and sequence features such as reduced complexity and repeated dinucleotides. These regions often display distinct structural properties, such as altered minor groove geometry and a tendency toward DNA bending. Such features can influence chromatin organization, replication timing, and transcriptional regulation, and AT-rich segments are sometimes associated with regulatory elements, repetitive elements, or noncoding regions.

Identification and analysis of AT-rich regions usually involve calculating nucleotide composition across the genome using sliding windows, then applying criteria for what constitutes “high AT content” or “low GC content.” These analyses can be affected by sequencing biases and assembly quality, particularly in regions with repeats or low complexity.

Biological significance varies by organism. In bacteria and archaea, AT-rich zones can affect origins of replication and promoter architecture; in eukaryotes, they can relate to chromatin accessibility and recombination patterns. In synthetic biology and genome engineering, AT-rich sequences are used to tune expression or control assembly, but their instability and propensity for slippage require careful design.

See also: GC content, genome composition, repetitive DNA.