Chemical synthesis and translesion replication of a cis-syn cyclobutane thymine-uracil dimer.
The cytosine base in DNA undergoes hydrolytic deamination at a considerable rate when UV radiation induces formation of a cyclobutane pyrimidine dimer (CPD) with an adjacent pyrimidine base. We have synthesized a phosphoramidite building block of a cis-syn cyclobutane thymine-uracil dimer (T[]U), which is the deaminated form of the CPD at a TC site, and incorporated it into oligodeoxyribonucleotides. The previously reported method for synthesis of the thymine dimer (T[]T) was applied, using partially protected thymidylyl-(3'-5')-2'-deoxyuridine as the starting material, and after triplet- sensitized irradiation, the configuration of the base moiety in the major product was determined by NMR spectroscopy. Presence of the cis-syn cyclobutane dimer in the obtained oligonucleotides was confirmed by UV photoreversal and reaction with T4 endonuclease V. Using a 30mer containing T[]U, translesion synthesis by human DNA polymerase eta was analyzed. There was no difference in the results between the templates containing T[]T and T[]U and pol eta bypassed both lesions with the same efficiency, incorporating two adenylates. This enzyme showed fidelity to base pair formation, but this replication causes a C-->T transition because the original sequence is TC.
Takasawa
Kohei
K
Division of Chemistry, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
Masutani
Chikahide
C
Hanaoka
Fumio
F
Iwai
Shigenori
S
D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D006801:Humans; D009838:Oligodeoxyribonucleotides / Q000096:biosynthesis / Q000138:chemical synthesis / Q000737:chemistry; D011740:Pyrimidine Dimers / Q000138:chemical synthesis* / Q000737:chemistry; D013941:Thymine / Q000737:chemistry; D014498:Uracil / Q000737:chemistry*; D000099270:Y-Family DNA Polymerases
D004259:DNA-Directed DNA Polymerase; D009838:Oligodeoxyribonucleotides; D011740:Pyrimidine Dimers; D013941:Thymine; D014498:Uracil; C112338:Rad30 protein; D000099270:Y-Family DNA Polymerases