DNA's Encounter with Ultraviolet Light: An Instinct for Self-Preservation?

Area of Science:

• Biochemistry
• Molecular Biology
• Evolutionary Biology

Background:

• DNA is susceptible to photochemical damage, primarily from UV light, forming pyrimidine dimers.
• Photolyases are enzymes that directly repair these dimers through photoreactivation.
• The RNA world hypothesis suggests early life used RNA for both genetic and catalytic functions.

Purpose of the Study:

• To investigate the possibility of creating catalytic nucleic acids with photolyase activity.
• To explore DNA enzymes (DNAzymes) capable of repairing UV-induced DNA damage.

Main Methods:

• In vitro selection from random-sequence DNA pools to identify DNAzymes.
• Characterization of DNAzyme kinetics, cofactor requirements, and substrate specificity.
• Structural analysis of active DNAzyme components, such as guanine quadruplexes.
• Spectroscopic analysis to determine action spectra and quantum yields.

Main Results:

• Two DNAzymes, Sero1C and UV1C, were discovered with DNA repair capabilities.
• UV1C, a cofactor-independent DNAzyme, repairs thymine dimers using light (300-310 nm) with a quantum yield comparable to some photolyases.
• UV1C's catalytic core involves a guanine quadruplex, hypothesized to facilitate electron transfer for photoreactivation.
• Sero1C demonstrated a broader substrate range for pyrimidine dimer repair compared to UV1C.

Conclusions:

• DNAzymes can be engineered to possess photolyase-like activity, repairing UV-induced DNA damage.
• The guanine quadruplex in UV1C provides a potential nucleotide-based mechanism for DNA photoreactivation.
• Nucleotide-based photoreactivation may have played a role in early life's protection against UV radiation in an RNA world.
• Engineered DNAzymes offer insights into the evolution of DNA repair mechanisms and the capabilities of nucleic acids.