Carlos A. Casiano Torres

Bio: Carlos A. Casiano Torres is an academic researcher from University of Puerto Rico, Río Piedras. The author has contributed to research in topics: Flash photolysis & DNA polymerase I. The author has an hindex of 3, co-authored 3 publications receiving 62 citations.

Part I. Photochemical and Photophysical Studies of Guanine Derivatives: Intermediates Contributing to its Photodestruction Mechanism in Aqueous Solution and the Participation of the Electron Adduct

Abstract: The low-intensity steady-state (254 nm), microsecond flash and nanosecond (266 nm) laser photolysis of some guanine (Gua) derivatives in aqueous solution were studied. A photodestruction yield between 10 23 and 10 22 at a base concentration of 75 mM was determined for 254 nm irradiation at room temperature using high-performance liquid chromatography. This yield decreases with increasing purine concentration. For a similar concentration of the purine bases (2 6 1) 3 10 25 M, the yield increases as follows: Gua 9-ethylguanine , deoxyguanosine guanosine (Guo) , guanosine 59-monophosphate. At concentrations higher than 2 3 10 24 M the Gua derivatives’ photodestruction yield seems to converge to a limiting value of the order of 10 24 . This behavior is explained in terms of self-quenching and aggregation effects which deactivate the excited states of the bases. The yields of electron photoejection have been determined in the nanosecond laser photolysis (0.083) and in the lowintensity steady-state (5.8 3 10 23 ) for Guo. Competition experiments using electron scavengers suggest that the electron adducts of the bases are one of the principal species participating in the photodestruction mechanism of these monomeric Gua. Close to 75% of the total destruction yield has contributions from initial reactions of the photojected electron at neutral pH. The quantum yield of photodestruction of Guo increases when the pH is increased as follows: 4.7 3 10 23

Intermediates in the room temperature flash photolysis and low temperature photolysis of purine solutions

Abstract: — The flash photolysis of purine in acetonitrile and in water at different pH was studied. The transients produced on flash excitation of degassed aqueous solutions have been identified as the triplet excited state, the hydrated electron, a purine radical cation and radical anion on the basis of quenching experiments and comparison to transients observed in low temperature photolysis.

Four-color dna sequencing by synthesis using cleavable fluorescent nucleotide reversible terminators

Abstract: This invention provides a process for sequencing single-stranded DNA employing modified nucleotides.

Massive parallel method for decoding DNA and RNA

Abstract: This invention provides methods for attaching a nucleic acid to a solid surface and for sequencing nucleic acid by detecting the identity of each nucleotide analogue after the nucleotide analogue is incorporated into a growing strand of DNA in a polymerase reaction. The invention also provides nucleotide analogues which comprise unique labels attached to the nucleotide analogue through a cleavable linker, and a cleavable chemical group to cap the —OH group at the 3′-position of the deoxyribose.

Inhibitors of protein synthesis identified by a high throughput multiplexed translation screen

Abstract: The use of small molecule inhibitors of cellular processes is a powerful approach to understanding gene function that complements the genetic approach. We have designed a high throughput screen to identify new inhibitors of eukaryotic protein synthesis. We used a bicistronic mRNA reporter to multiplex our assay and simultaneously screen for inhibitors of cap-dependent initiation, internal initiation and translation elongation/termination. Functional screening of >90 000 compounds in an in vitro translation reaction identified 36 inhibitors, 14 of which are known inhibitors of translation and 18 of which are nucleic acid-binding ligands. Our results indicate that intercalators constitute a large class of protein synthesis inhibitors. Four non-intercalating compounds were identified, three of which block elongation and one of which inhibits initiation. The novel inhibitor of initiation affects 5' end-mediated initiation, as well as translation initiated from picornaviral IRESs, but does not significantly affect internal initiation from the hepatitis C virus 5'-untranslated region. This compound should be useful for delineating differences in mechanism of initiation among IRESs.

Interaction of Triplet Photosensitizers with Nucleotides and DNA in Aqueous Solution at Room Temperature

Abstract: The study of triplet excited state behavior of nucleic acids and component mononucleotides is hampered by the very small yields produced by direct photolysis. We have used high energy triplet sensitizers to generate these species in high yield, thus facilitating the study of their photophysical and photochemical behavior. Acetone-sensitized triplet formation of all triplet state nucleotides allowed nucleotide triplet−triplet absorption spectra to be measured. Triplet−triplet absorption coefficients were determined using comparative actinometry. Self-quenching of the nucleotide triplet states was found to occur efficiently with rate constants, ksq > 107 M-1 s-1. The interaction of a variety of ketone triplet sensitizers with mononucleotides has been studied as a function of the relative energies of the sensitizer−nucleotide pair. In all cases, the triplet states of the sensitizers were efficiently quenched by the nucleotides, although different reaction mechanisms were observed depending on the reaction pa...