Replication slippage and the dynamics of the immune response in malaria: a formal model for immunity.

A simple mathematical model of the dynamics of malaria invasion is proposed. The model is based on the hypothesis that replication slippage (slipped strand mispairing occurring in replicating DNAs), likely to take place within regular, low-complexity, regions of the plasmodium genome, is a significant mechanism of the ability for the parasite to escape the host immune defence. The model reconciles the conclusions of other formal approaches like periodic bursts of parasitaemia and, in particular, it predicts that antibody cross-reactivity affects the level and the time profile of malaria recrudescence. It also suggests that an efficient strategy for the parasite to escape host humoral immune defences is to express a single antigen. Linking local complexity to antigenic variability tentatively allows prediction of new potentially immunogenic sequences in the plasmodium genome.

Fourier and wavelet transform analysis, a tool for visualizing regular patterns in DNA sequences.

A correlation function that compares each base in a DNA sequence to its various neighbours and which is subsequently processed by Fourier and wavelet transforms has been developed. The procedure has been applied to sequences from the human chromosome 22, to nef genes from various HIV clones and to myosin heavy chain DNA. It permits to readily visualize regular features in DNA which are related to the stability of heteroduplexes formed upon strand slippage.

[Not Available]. / Unite d'acquisition economique pour le traitement elabore de donnees spectro-cinetiques issues d'un spectrophotometre UV-visible.

A low-cost digital acquisition unit for a CARY-210 spectrophotometer has been designed and constructed. The data-flow is controlled by a 6809 microprocessor driving four parallel interface adapters. Two RS232-C serial links are provided for communication with a terminal and a mass storage unit. The acquired data are processed by a personal computer. Included are several software modules, based on powerful signal-processing algorithms, which are highly useful in kinetic studies.

[Not Available]. / Systeme d'analyse et d'acquisition de donnees cinetiques pilote par microprocesseur.

This paper describes a low-cost 6809 microprocessor-based system designed for the acquisition, analysis, preprocessing and recording of electrochemical kinetic data. Determination of second-order rate constants involves a preliminary calculation of a characteristic parameter of the electro-chemical system investigated, the value of which, computed and displayed by our apparatus, allows checking of the correctness of the experimental conditions. At the end of the experiment the data are recorded on a magnetic tape cartridge and can be transferred from the tape to a minicomputer for further mathematical processing.

Highly sensitive microwave temperature-jump apparatus.

A temperature-jump apparatus with repetitive microwave heating and spectrophotometric detection is described. Temperature jumps of 1.5 degrees C are achieved in a flow microcell within 1.5 mus (two shorter heating times of 0.5 and 0.25 mus are also available) at a repetition rate up to 50 Hz. On-line accumulation of the relaxation signals is performed with a PDP 11 processor, leading to very short recording times (more than 1000 signals accumulated in less than 50 s) and to a sensitivity better than 10(-4) optical density (OD) units. Nonlinear identification treatment permits processing the summed signal even when it is strongly blurred by noise. To demonstrate the capabilities of our apparatus, highly shifted fast prototropic equilibria in aqueous solutions of pyrimidine base have been studied.