Thymine glycol severely inhibits DNA synthesis by replicativ

Thymine glycol severely inhibits DNA synthesis by replicative DNA polymerases and requires the action of specialized DNA polymerases for translesion synthesis (e.g. Ref. [26]). Eukaryotic and archaeal RNAPs were shown to pause after nucleotide insertion opposite TG [27,28]. Surprisingly, we found that transcription by bacterial RNAP is only slightly affected by this modification, probably because the RNAP active site is more tolerant to the duplex distortion caused by the nonplanar TG configuration, suggesting that this lesion may not be a subject for TCR. Finally, we analyzed several substitutions of amino apexbio calculator residues in the RNAP active site involved in direct interactions with the transcribed DNA strand. Unexpectedly, some of these substitutions (R542A, Y795A and R798A) lacked any prominent effects on transcription of both normal and damaged DNA templates, despite affecting conserved RNAP residues involved in template interactions. At the same time, two substitutions, K334A in switch2 and T790 in the BH, inhibited transcription, and this effect was exacerbated on most damaged templates. The T790A substitution was previously shown to decrease RNAP activity in a number of assays, possibly by changing the BH conformation and/or its contacts with the template-NTP pair [29], likely explaining its effects on translesion synthesis. The effect of the K334A substitution may result from changes in RNAP contacts with the template DNA strand downstream of the active site and in the conformation of the clamp domain that holds the DNA-RNA duplex [14]. At the same time, the K334A substitution stimulated transcription past CPD, in contrast to other lesions, suggesting that it may help to overcome transcription stalling caused by this bulky lesion, possibly by loosening RNAP-DNA contacts near the active site.
Acknowledgements We thank I. Artsimovitch for plasmids and for the CPD template. This work was supported by the Grant of the Ministry of Higher Education and Science of the Russian Federation 14.W03.31.0007.
Introduction Cancer is the second cause of death and responsible for one-sixth of the deaths (estimated 9.6 million) all over the world in 2018 [1]. And the International Agency for Research on Cancer (IARC) estimated that there would be 21.7 million new cancer cases and 13 million cancer deaths by 2030 [2]. The development of new cancer treatments and drugs have been attracted great attention for decades. In 2017, FDA approved 12 oncology products which were 26% of the approved products [3]. Organometallic compounds exhibited remarkable potential for the development of new cancer drugs not only due to the direct cytotoxicity but also to the drug targeting and active anticancer immune response ability [4]. Among the organometallic compounds, ferrocene is one of the most well-known compounds in many areas of science, especially in medicinal chemistry. It attracted great attention on account of the high stability, lipophilicity, low toxicity, easy functionalization and mild reversible redox property [5]. Hence, ferrocenyl group conjugated nature products or drugs were synthesized and exhibited kinds of biological activities, including antitumor, antimalarial and antibacterial activity [6]. In the development of ferrocene based drugs, the two most successful examples were ferrocifen and ferroquine. The last one entered the clinical trials and would be completed in 2019 [7]. The two compounds represent one type of ferrocene derivatives, in which the ferrocenyl group replaced a portion of the lead compound [8]. And in another type, the ferrocenyl group directly attached to the lead compound, which is a promising strategy to enhance the anticancer efficiency by attaching ferrocenyl group to a DNA intercalator [5a]. Ferrocene appended intercalators were reported to exhibit far more cytotoxicity or better selectivity towards cancerous cells than the single intercalators [9].