[Common features in arrangements of ribosomal protein S26e binding sites on its own pre-mRNA and the 18S rRNA]

It is known that human ribosomal protein (rp) S26e can bind to the first intron of its own pre-mRNA and thereby inhibit its splicing. In this work, hydroxyl radical footprinting was applied for detailed mapping of the rpS26e binding site on an RNA transcript corresponding to the rpS26e pre-mRNA fragment containing the first intron flanked by the first exon and a part of the second exon sequences. Nucleotides of this RNA protected from hydroxyl radical attack in the presence of rpS26e were identified. Most of them are found in the region of the 3'-splice site of the first intron within a purine-rich sequence, which forms a loop connecting two helices in the predicted secondary structure of the rpS26e pre-mRNA fragment, and the remaining nucleotides are located near the 5'-splice site. Comparison of arrangements of rpS26e binding sites on the pre-mRNA and 18S rRNA secondary structures reveals similar elements in the organization of these sites. It was found that both sites contain a structural motif, represented by an extended purine-rich loop between two helices, which could be recognized by rpS26e upon binding to these RNAs. The data obtained shed light on the structural aspects of RNA-protein interactions underlying autoregulation of human RPS26e gene expression at the splicing step.