RESUMO
Chromatin structure of so-called 'Alu-repeat' in D. melanogaster ribosomal non-transcribed spacer that contains sequences homologous to the promoter of ribosomal genes has been studied. Using the 'protein image' hybridization assay based on UV-light-induced DNA-protein crosslinking and 2-D gel retardation electrophoresis, two proteins of the molecular mass of 50 kD (rABP50) and 70 kD (rABP70), associated with 'Alu-repeat' DNA have been found. Exo III mapping of crosslinking sites and DNase I footprinting have provided a detailed map of H1, rABP50 and rABP70 contacts within the 'Alu-repeat' and H1 and a non-histone protein contacts on satellite DNA. These data indicate precise positioning of non-histone proteins, histone H1 and nucleosomes within genomic regions studied and account for the presence of unusual 240 bp long nucleosomal particles in 'Alu-repeats'. The same approach can be adapted for successive mapping and positioning proteins on genomic DNA.
