부산대학교 도서관

rRNA is the single most abundant polymer in most cells. Mammalian rRNAs are nearly twice as large as those of prokaryotes. Differences in rRNA size are due to expansion segments, which contain extended tentacles in metazoans. Here we show that the terminus of an rRNA tentacle of Homo sapiens contains 10 tandem G-tracts that form highly stable G-quadruplexes in vitro. We characterized rRNA of the H. sapiens large ribosomal subunit by computation, circular dichroism, UV melting, fluorescent probes, nuclease accessibility, electrophoretic mobility shifts, and blotting. We investigated Expansion Segment 7 (ES7), oligomers derived from ES7, intact 28S rRNA, 80S ribosomes, and polysomes. We used mass spectrometry to identify proteins that bind to rRNA G-quadruplexes in cell lysates. These proteins include helicases (DDX3, CNBP, DDX21, DDX17) and heterogeneous nuclear ribonucleoproteins. Finally, by multiple sequence alignments, we observe that G-quadruplex-forming sequences are a general feature of LSU rRNA of Chordata but not, as far as we can tell, of other species. Chordata ribosomes present polymorphic tentacles with the potential to switch between inter- and intramolecular G-quadruplexes. To our knowledge, G-quadruplexes have not been reported previously in ribosomes. Unlabelled Image • Human ribosomal RNA can form G-quadruplexes in vitro. • Human G-quadruplex-forming regions are located near the termini of rRNA tentacles of expansion segments 7 and 27 and are exposed on the ribosomal surface. • Their surface localization suggests potential functions on non-ribosomal protein recruitment and/or polysome assembly. • G-quadruplex-forming rRNA sequences are observed throughout the phylum Chordata. [ABSTRACT FROM AUTHOR]