Pyrimidine dimers represent molecular lesions originating from thymine or cytosine bases within DNA, resulting from photochemical reactions. [1][2] These lesions, commonly linked to direct DNA damage, [3] are induced by ultraviolet light (UV), particularly UVC, result in the formation of covalent bonds between adjacent nitrogenous bases along th...

Femtosecond time-resolved infrared spectroscopy is used to study the formation of cyclobutane dimers in the all-thymine oligonucleotide (dT) 18 by ultraviolet light at 272 nanometers. The appearance of marker bands in time-resolved spectra indicate that dimers are fully formed ∼1 picosecond after ultraviolet excitation.

Since the discovery of thymine–thymine (TT) dimer, there has been intense research on the mechanism of this fundamental process [117, 118]. The typical quantum yield of dimerization in DNA is <1%.

The most common reaction is shown here: two thymine bases have formed a tight thymine dimer, with two bonds gluing the bases together. The upper image is from PDB entry 1n4e and the close-up picture at the bottom is from PDB entry 1ttd .

Thymidine Dimers are produced when adjacent thymidine residues are covalently linked by exposure to ultraviolet radiation. Covalent linkage may result in the dimer being replicated as a single base, which results in a frameshift mutation.

The most common covalently linked adjoining pyrimidines are T-T (thymine dimers), T-C (thymine-cytosine dimers) and C-C (cytosine-cytosine dimers). T-T dimers cause kinks in the DNA strand that prevent both replication and transcription of that part of the DNA.

Synergistic modulation of cyclobutane pyrimidine dimer photoproduct formation and deamination at a TmCG site over a full helical DNA turn in a nucleosome core particle.

Oct 21, 2011 · In particular, photoinduced thymine-thymine (TT) dimer formation has been found to be a picosecond process. The most prevalent TT dimer is formed by a [2+2] addition of the C5–C6 double bonds of the dimerizing thymines.

Jan 1, 2009 · Pyrimidine dimer in DNA. A TT dimer (in violet) is shown within a DNA double helix. Notice the four-membered cyclobutane ring formed between the two thymine bases. The dimer causes local distortions in the helix, weakening the interaction with the paired adenine bases and kinking the backbone slightly.

T^T dimers may be repaired by two mechanisms. (a) In photoreactivation repair, the PRE enzyme activated by blue light breaks the dimer, restoring the normal base pairing. Note that blue light can affect DNA because it is at the same end of the spectrum as UV radiation.