Plasmodium gallinaceum: induction of male gametocyte exflagellation by phosphodiesterase inhibitors.

The phosphodiesterase inhibitors, Squibb 20009, caffeine, and 8-bromo-cyclic adenosine monophosphate (8-bromo-cAMP) are capable of stimulating gametogenesis, thus implicating cyclic nucleotides in the initiation of this process. Squibb 20009 and 8-bromo-cAMP stimulated gametogenesis at pH 8.0 but not at pH 7.4 whereas caffeine stimulated gametogenesis at pH 8.0 and 7.4.     

A simple method for studying the solubilization of polycyclic aromatic hydrocarbons in DNA solutions

A simple method for detecting the amount of a polycyclic aromatic hydrocarbon (PAH) solubilized in DNA solutions is described. This method takes advantage of the fact that sodium dodecyl sulfate (SDS) induces dissociation of PAH from DNA, and the greatly enhanced solubility of PAH in SDS solution makes possible the direct preparation of a standard solution for the extinction coefficient determination. The ability to make direct comparison between the spectroscopic characteristics before and after dissociation is accomplished by utilizing a tandem cuvette. The usefulness of this technique is then demonstrated by applying it to solubilization studies of pyrene in native and denatured DNA solutions of varying sodium chloride concentrations as well as in deoxymononucleotide solutions. Binding constants are estimated and the solubility data for pyrene in the DNA solutions are interpreted in terms of the binding abilities of intercalative versus external sites and the effect of salt. The mononucleotide results suggest a binding preference of pyrene to purine bases. It was observed that the binding constant of mononucleotide to pyrene is an order of magnitude lower than that of single-stranded DNA, which in turn is an order of magnitude smaller than that of duplex DNA.     

Role of pyrimidine salvage pathway in the maintenance of organellar and nuclear genome integrity

Nucleotide biosynthesis proceeds through a de novo pathway and a salvage route. In the salvage route, free bases and/or nucleosides are recycled to generate the corresponding nucleotides. Thymidine kinase (TK) is the first enzyme in the salvage pathway to recycle thymidine nucleosides as it phosphorylates thymidine to yield thymidine monophosphate. The Arabidopsis genome contains two TK genes ?TK1a and TK1b? that show similar expression patterns during development. In this work, we studied the respective roles of the two genes during early development and in response to genotoxic agents targeting the organellar or the nuclear genome. We found that the pyrimidine salvage pathway is crucial for chloroplast development and genome replication, as well as for the maintenance of its integrity, and is thus likely to play a crucial role during the transition from heterotrophy to autotrophy after germination. Interestingly, defects in TK activity could be partially compensated by supplementation of the medium with sugar, and this effect resulted from both the availability of a carbon source and the activation of the nucleotide de novo synthesis pathway, providing evidence for a compensation mechanism between two routes of nucleotide biosynthesis that depend on nutrient availability. Finally, we found differential roles of the TK1a and TK1b genes during the plant response to genotoxic stress, suggesting that different pools of nucleotides exist within the cells and are required to respond to different types of DNA damage. Altogether, our results highlight the importance of the pyrimidine salvage pathway, both during plant development and in response to genotoxic stress.