The Cell Cycle Regulated Transcriptome of Trypanosoma brucei

Progression of the eukaryotic cell cycle requires the regulation of hundreds of genes to ensure that they are expressed at the required times. Integral to cell cycle progression in yeast and animal cells are temporally controlled, progressive waves of transcription mediated by cell cycle-regulated transcription factors. However, in the kinetoplastids, a group of early-branching eukaryotes including many important pathogens, transcriptional regulation is almost completely absent, raising questions about the extent of cell-cycle regulation in these organisms and the mechanisms whereby regulation is achieved. Here, we analyse gene expression over the Trypanosoma brucei cell cycle, measuring changes in mRNA abundance on a transcriptome-wide scale. We developed a “double-cut” elutriation procedure to select unperturbed, highly synchronous cell populations from log-phase cultures, and compared this to synchronization by starvation. Transcriptome profiling over the cell cycle revealed the regulation of at least 430 genes. While only a minority were homologous to known cell cycle regulated transcripts in yeast or human, their functions correlated with the cellular processes occurring at the time of peak expression. We searched for potential target sites of RNA-binding proteins in these transcripts, which might earmark them for selective degradation or stabilization. Over-represented sequence motifs were found in several co-regulated transcript groups and were conserved in other kinetoplastids. Furthermore, we found evidence for cell-cycle regulation of a flagellar protein regulon with a highly conserved sequence motif, bearing similarity to consensus PUF-protein binding motifs. RNA sequence motifs that are functional in cell-cycle regulation were more widespread than previously expected and conserved within kinetoplastids. These findings highlight the central importance of post-transcriptional regulation in the proliferation of parasitic kinetoplastids

Effect of organized assemblies. Part I-Effect of variation in chain length of carboxy and alkoxy end of esters on the hydrolysis of simple aliphatic esters

258-264The hydrolysis of some simple aliphatic esters having variation in number of carbon atoms in their alkoxy and carboxy part has been carried out in presence of ionic and non-ionic micelles to investigate the effect of the subsequent change in chain length on the mechanism of hydrolysis of esters. The effect of variation of temperature, concentration of salt, substrate, surfactant, and acid has also been examined. The results have been ascribed to the role of the charge of surfactants and partitioning of the substrate into the surfactant aggregates

Organization of amphiphiles Part-X: Studies on the interaction between polyoxyethylated (30) octylphenol and cetyltrimethylammonium bromide in aqueous solution

The solution behavior of the mixture of cetyltrimethylammonium bromide (CTAB) and polyoxyethylene (30) octylphenol (OP-30) has been investigated by measuring the conductance, fluorescence intensity, surface tension and absorbance of the surfactant mixtures. A strong interaction between the two surfactants is indicated from each of the measurements. The critical micelle concentration of CTAB is found to increase with increase in the amount of OP-30 in the mixture. This delaying in micellization of CTAB has been attributed to the diminution of its effective hydrophobicity due to interaction with monomers or micelles of OP-30. Below CMC of OP-30, the monomeric concentration of CTAB decreases due to the formation of a hydrophobic complex between OP-30 and CTAB. Above CMC of OP-30, CTAB monomers get solubilized into micellar core of OP-30 in 1:1 stoichiometric ratio. Micropolarity and the aggregation numbers of the mixed systems have been determined from fluorescence studies. The thermodynamics of micelle formation of CTAB coupled with fluorescence studies of the mixtures indicates that the complex grows in size with increase of OP-30 concentration till the micelle of latter is formed at higher concentrations. The treatment of theoretical model to the interaction of OP-30 and CTAB yields a positive interaction parameter showing antagonism behavior. A schematic model of interaction of OP-30 with CTAB below and above its CMC has been suggested

Effect of organized assemblies, Part-III: Micellar catalysed iodo-de-diazoniation reactions

2140-2142The iodo-de-diazoniation of benzene diazonium chloride has been carried out in the presence of ionic and nonionic surfactants. Anionic and nonionic micelles do not facilitate the product formation whereas the cationic surfactant gives a reasonable increase in the yield as compared to that in the absence of the surfactants. The results have been attributed to the increase in the effective concentration of the reactants in a reduced volume of Menger’s micelle resulting out of both hydrophobic and electrostatic interaction of the reactants and the micelle