Escherichia coli MutY protein has a guanine-DNA glycosylase that acts on 7,8-dihydro-8-oxoguanine:guanine mispair to prevent spontaneous G:C-->C:G transversions

Low rates of spontaneous G:C-->C:G transversions would be achieved not only by the correction of base mismatches during DNA replication but also by the prevention and removal of oxidative base damage in DNA. Escherichia coli must have several pathways to repair such mismatches and DNA modifications. In this study, we attempted to identify mutator loci leading to G:C-->C:G transversions in E.coli. The strain CC103 carrying a specific mutation in lacZ was mutagenized by random miniTn 10 insertion mutagenesis. In this strain, only the G:C-->C:G change can revert the glutamic acid at codon 461, which is essential for sufficient beta-galactosidase activity to allow growth on lactose. Mutator strains were detected as colonies with significantly increased rates of papillae formation on glucose minimal plates containing P-Gal and X-Gal. We screened approximately 40 000 colonies and selected several mutator strains. The strain GC39 showed the highest mutation rate to Lac+. The gene responsible for the mutator phenotypes, mut39 , was mapped at around 67 min on the E.coli chromosome. The sequencing of the miniTn 10 -flanking DNA region revealed that the mut39 was identical to the mutY gene of E.coli. The plasmid carrying the mutY + gene reduced spontaneous G:C-->T:A and G:C-->C:G mutations in both mutY and mut39 strains. Purified MutY protein bound to the oligonucleotides containing 7,8-dihydro-8-oxo-guanine (8-oxoG):G and 8-oxoG:A. Furthermore, we found that the MutY protein had a DNA glycosylase activity which removes unmodified guanine from the 8-oxoG:G mispair. These results demonstrate that the MutY protein prevents the generation of G:C-->C:G transversions by removing guanine from the 8-oxoG:G mispair in E.coli.     

Polarization ellipse and Stokes parameters in geometric algebra

In this paper, we use geometric algebra to describe the polarization ellipse and Stokes parameters. We show that a solution to Maxwell's equation is a product of a complex basis vector in Jackson and a linear combination of plane wave functions. We convert both the amplitudes and the wave function arguments from complex scalars to complex vectors. This conversion allows us to separate the electric field vector and the imaginary magnetic field vector, because exponentials of imaginary scalars convert vectors to imaginary vectors and vice versa, while exponentials of imaginary vectors only rotate the vector or imaginary vector they are multiplied to. We convert this expression for polarized light into two other representations: the Cartesian representation and the rotated ellipse representation. We compute the conversion relations among the representation parameters and their corresponding Stokes parameters. And finally, we propose a set of geometric relations between the electric and magnetic fields that satisfy an equation similar to the Poincaré sphere equation.     

High-performance liquid chromatography of amino acids, peptides and proteins. CXXXIX. Impact of operating parameters in large-scale chromatography of proteins

Large-scale chromatography has been playing an important role in downstream treatment processing in biotechnology. In order to improve the productivity, the throughput of the chromatographic equipment was often increased by increasing the flow-rate and/or by increasing the column sample loading. This paper reports the results of a study on the impact of these and other operating parameters in affinity and ion-exchange chromatographic columns when used for protein purification. A sectional model was developed to predict protein adsorption processes in a packed column. The formulations of this mathematical model are presented in the Appendix. The present study was carried out with computer simulation based on this model and using data obtained from laboratory-scale columns. This model can simulate both the adsorption and washing stages of the protein purification process for both porous and non-porous particles. The effects of changing operating parameters were simulated and contour plots were generated for the easy identification of these effects. It was shown that both flow-rate and column loading can have a considerable impact on the processing rate and the yield of the column. As for the column capacity utilization, the impact of changing flow-rate is not significant at column loading of less than 80% in the test case. It was suggest that the present investigation provides a systematic predictive strategy which will greatly reduce the need for expensive, labour-intensive and time-consuming experimental work during process scale-up.