At the same time, low photochemical activity and stability of 5,10-methenyltetrahydrofolic acid (MTHF) against photochemical oxidation is a prerequisite for non-radiative energy transfer from this Selumetinib order excited molecule and may have favored a selection

of this molecule for light-harvesting antenna in photoreceptor proteins DNA-photolyase and cryptochrome (Sancar, 2003). The other properties essential for selection of MTHF for antenna pigment were high photon absorptivity (the ɛ max = 26,000 M−1) and the long-wave shifted absorption maximum (λ max = 360 nm) as compared to other H4-folates. The combination of these properties in MTHF results from the CP673451 datasheet presence in its molecule of imidazoline ring adjacent to pteridine heterocycle and the protonated state of tetrahydropteridine cycle (Telegina et al., 2005). Interestingly, MTHF was conserved as antenna pigment in light-sensitive proteins of eukaryotic organisms whose find more evolution proceeded in oxygen-rich atmosphere. At the same time, in some prokaryotes including

archea and cyanobacteria, another compound, 7,8-didemethyl-8-hydroxy-5-deazariboflavin plays this role in DNA photolyases (Sancar, 2003). Unlike deazaflavin, found only in few microbial species, MTHF is a participant of cell metabolism in a variety of pro- and eukaryotic organisms. Supported by Program of Basic Research No 18 of Russian Academy of Sciences and by grants NoNo 07-04-00460_a and 06-04-90599-BNTS_a from Russian Foundation for Basic Research. Heinz, B., Ried, W., Dose, K. (1979). Thermische Erzeugung von Pteridinen und Flavinen aus Aminosaueregemischen. Angewandte Chemie, 91(6):510–511 Kritsky, M.S. and Telegina, T.A. (2004). Role of nucleotide-like coenzymes in primitive evolution. In Seckbach J., editor, Origins Genesis, Evolution and Diversity of Life, pages 215–231. Kluwer, Dordrecht. Sancar, A. (2003). Structure and function of DNA photolyase and cryptochrome blue-light photoreceptors. Chemical Vitamin B12 Reviews. 103:2203–2237 Telegina, T. A., Lyudnikova,

T. A., Zemskova, Yu. L., Sviridov, E. A., and Kritsky, M. S. (2005). Resistance of 5,10-methenyltetrahydrofolate to ultraviolet radiation. Applied Biochemistry and Microbiology. 41(3):275–282 E-mail: vechtomova@inbi.​ras.​ru Low Complexity in Regions in Lentiviral Proteins Ana Maria Velasco, Luis Delaye, Arturo Becerra, Antonio Lazcano Facultad de Ciencias, UNAM, Apdo. Postal 70–407, Ciudad Universitaria, Mexico D. F. 04510, MEXICO The presence of low complexity regions (LCR) has been confirmed in sequences of the three cellular linages (Bacteria, Archaea and Eucarya). Nevertheless, the role that they play is not yet fully understood. Much less is know about viral LCRs.