Chemiexcited Neurotransmitters and Hormones Create DNA Photoproducts in the Dark.

In DNA, electron excitation allows adjacent pyrimidine bases to dimerize by [2 + 2] cycloaddition, creating chemically stable but lethal and mutagenic cyclobutane pyrimidine dimers (CPDs). The usual cause is ultraviolet radiation. Alternatively, CPDs can be made in the dark (dCPDs) via chemically mediated electron excitation of the skin pigment melanin, after it is oxidized by peroxynitrite formed from the stress-induced radicals superoxide and nitric oxide.

Triplet-Energy Quenching Functions of Antioxidant Molecules.

UV-like DNA damage is created in the dark by chemiexcitation, in which UV-activated enzymes generate reactive oxygen and nitrogen species that create a dioxetane on melanin. Thermal cleavage creates an electronically excited triplet-state carbonyl whose high energy transfers to DNA. Screening natural compounds for the ability to quench this energy identified polyenes, polyphenols, mycosporine-like amino acids, and related compounds better known as antioxidants.

Genomic sites hypersensitive to ultraviolet radiation.

If the genome contains outlier sequences extraordinarily sensitive to environmental agents, these would be sentinels for monitoring personal carcinogen exposure and might drive direct changes in cell physiology rather than acting through rare mutations. New methods, adductSeq and freqSeq, provided statistical resolution to quantify rare lesions at single-base resolution across the genome. Primary human melanocytes, but not fibroblasts, carried spontaneous apurinic sites and TG sequence lesions more frequent than ultraviolet (UV)-induced cyclobutane pyrimidine dimers (CPDs).

Conservative evolution in duplicated genes of the primate Class I ADH cluster.

Humans have seven alcohol dehydrogenase genes (ADH) falling into five classes. Three out of the seven genes (ADH1A, ADH1B and ADH1C) belonging to Class I are expressed primarily in liver and code the main enzymes catalyzing ethanol oxidization. The three genes are tandemly arrayed within the ADH cluster on chromosome 4 and have very high nucleotide similarity to each other (exons: >90%; introns: >70%), suggesting the genes have been generated by duplication event(s).

Population variation in linkage disequilibrium across the COMT gene considering promoter region and coding region variation.

Catechol-O-methyl transferase (COMT) catalyzes the first step in one of the major pathways in the degradation of catecholamines. The COMT gene on chromosome 22 has been considered a candidate gene for many neuropsychiatric disorders, in part because an exon 4 single nucleotide polymorphism (SNP) in COMT causes an amino acid substitution associated with significantly altered enzyme activity. This functional variant, detected as an NlaIII restriction site polymorphism (RSP), is polymorphic in populations from around the world.