Moysan A, Viari A, Vigny P, Voituriez L, Cadet J, Moustacchi E, Sage E
Laboratoire de Physique et Chimie Biomoléculaire, CNRS UA 198, Institut Curie, Paris, France.
Biochemistry. 1991 Jul 23;30(29):7080-8. doi: 10.1021/bi00243a007.
As after irradiation with 254-nm UV light, exposure of thymidine and three isomeric pyridopsoralen derivatives to UVA radiation, in the dry state, leads to the formation of the six diastereomers of cyclobutadithymidine as the predominant reaction. This unexpected photosensitized reaction, which also gives rise to both 5R* and 5S* diastereomers of 5,6-dihydro-5-(alpha-thymidylyl)thymidine (or "spore" photoproduct), is selective since [2 + 2] dimerization of 2'-deoxycytidine was not detected under the same experimental conditions. The cis-syn isomer of cyclobutadithymine was also found to be produced within isolated DNA following UVA irradiation in aqueous solutions containing 7-methylpyrido[3,4-c]psoralen. Quantitatively, this photoproduct represents about one-fifth of the overall yield of the furan-side pyridopsoralen [2 + 2] photocycloadducts to thymine. DNA sequencing methodology was used to demonstrate that pyridopsoralen-photosensitized DNA is a substrate for T4 endonuclease V and Escherichia coli photoreactivating enzyme, two enzymes acting specifically on cyclobutane pyrimidine dimers. Furthermore, the dimerization reaction of thymine is sequence dependent, with a different specificity from that mediated by far-UV irradiation as inferred from gel sequencing experiments. Interestingly, adjacent thymine residues are excellent targets for 7-methylpyrido[3,4-c]psoralen-mediated formation of cyclobutadithymine in TTTTA and TTAAT sites, which are also the strongest sites for photoaddition. The formation of cyclobutane thymine dimers concomitant to that of thymine-furocoumarin photoadducts and their eventual implication in the photobiological effects of the pyridopsoralens are discussed.
在254纳米紫外光照射后，胸腺嘧啶核苷和三种异构的吡啶补骨脂素衍生物在干燥状态下暴露于UVA辐射，会导致环丁二硫代胸腺嘧啶核苷的六种非对映异构体形成，这是主要反应。这种意外的光敏反应还会产生5,6-二氢-5-(α-胸苷酰基)胸腺嘧啶核苷（或“孢子”光产物）的5R和5S非对映异构体，该反应具有选择性，因为在相同实验条件下未检测到2'-脱氧胞苷的[2 + 2]二聚化。在含有7-甲基吡啶并[3,4-c]补骨脂素的水溶液中进行UVA照射后，在分离的DNA中也发现了环丁二硫代胸腺嘧啶的顺式-顺式异构体。从数量上看，这种光产物约占呋喃侧吡啶补骨脂素与胸腺嘧啶的[2 + 2]光环化加成物总产率的五分之一。DNA测序方法被用于证明吡啶补骨脂素光敏化的DNA是T4内切核酸酶V和大肠杆菌光复活酶的底物，这两种酶专门作用于环丁烷嘧啶二聚体。此外，胸腺嘧啶的二聚化反应依赖于序列，其特异性与远紫外照射介导的不同，这是从凝胶测序实验推断出来的。有趣的是，相邻的胸腺嘧啶残基是7-甲基吡啶并[3,4-c]补骨脂素介导在TTTTA和TTAAT位点形成环丁二硫代胸腺嘧啶的极佳靶点，这些位点也是光加成最强的位点。本文讨论了环丁烷胸腺嘧啶二聚体与胸腺嘧啶-呋喃香豆素光加成物的形成及其最终在吡啶补骨脂素光生物学效应中的意义。
