title: Sequence requirements for maturation of the 5' terminus of human 18 S rRNA in vitro.
abstract: Creation of the mature 5' terminus of human 18 S rRNA in vitro occurs via a two-step processing reaction. In the first step, an endonucleolytic activity found in HeLa cell nucleolar extract cleaves an rRNA precursor spanning the external transcribed spacer-18 S boundary at a position 3 bases upstream from the mature 18 S terminus leaving 2',3'-cyclic phosphate, 5' hydroxyl termini. In the second step, a nucleolytic activity(s) found in HeLa cell cytoplasmic extract removes the 3 extra bases and creates the authentic 5'-phosphorylated terminus of 18 S rRNA. Here we have examined the sequence requirements for the trimming reaction. The trimming activity(s), in addition to requiring a 5' hydroxyl terminus, prefers the naturally occurring adenosine as the 5'-terminal base. By a combination of deletion, site-directed mutagenesis, and chemical modification interference approaches we have also identified a region of 18 S rRNA spanning bases +6 to +25 (with respect to the mature 5' end) which comprises a critical recognition sequence for the trimming activity(s).
authors.affiliation: Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4690.
authors.forename: Y T
authors.initials: YT
authors.lastname: Yu
authors.forename: T W
authors.initials: TW
authors.lastname: Nilsen
mesh_terms: D001483:Base Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012337:RNA, Ribosomal, 18S / Q000235:genetics* / Q000378:metabolism; D013379:Substrate Specificity; D013698:Templates, Genetic; D014158:Transcription, Genetic
chemical_list: D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S