Chromosomal integration of LTR-flanked DNA in yeast expressing HIV-1 integrase: down regulation by RAD51

HIV-1 integrase (IN) is the key enzyme catalyzing the proviral DNA integration step. Although the enzyme catalyzes the integration step accurately in vitro, whether IN is sufficient for in vivo integration and how it interacts with the cellular machinery remains unclear. We set up a yeast cellular integration system where integrase was expressed as the sole HIV-1 protein and targeted the chromosomes. In this simple eukaryotic model, integrase is necessary and sufficient for the insertion of a DNA containing viral LTRs into the genome, thereby allowing the study of the isolated integration step independently of other viral mechanisms. Furthermore, the yeast system was used to identify cellular mechanisms involved in the integration step and allowed us to show the role of homologous recombination systems. We demonstrated physical interactions between HIV-1 IN and RAD51 protein and showed that HIV-1 integrase activity could be inhibited both in the cell and in vitro by RAD51 protein. Our data allowed the identification of RAD51 as a novel in vitro IN cofactor able to down regulate the activity of this retroviral enzyme, thereby acting as a potential cellular restriction factor to HIV infection

A simple and efficient error-diffusion algorithm

In this contribution, we introduce a new error-diffusion scheme that produces higher quality results. The algorithm is faster than the universally used Floyd-Steinberg algorithm, while maintaining its original simplicity. The efficiency of our algorithm is based on a deliberately restricted choice of the distribution coefficients. Its pleasing nearly artifact-free behavior is due to the off-line minimization process applied to the basic algorithm’s parameters (distribution coefficients). This minimization brings the Fourier spectra of the selected key intensity levels as close as possible to the corresponding “blue noise ” spectra. The continuity of the algorithm’s behavior across the full range of intensity levels is achieved thanks to smooth interpolation between the distribution coefficients corresponding to key levels. This algorithm is applicable in a wide range of computer graphics applications, where a color quantization algorithm with good visual properties is needed