A role for upstream RNA structure in facilitating the catalytic fold of the genomic hepatitis delta virus ribozyme.
Hepatitis delta virus (HDV) has a circular RNA genome that replicates by a double rolling-circle mechanism. The genomic and antigenomic versions of HDV contain a ribozyme that undergoes cis-cleavage, thereby processing the transcript into unit-length monomers. A genomic HDV transcript containing 30 nucleotides immediately upstream of the cleavage site was found to have attenuated self-cleavage. Structure mapping and site-directed mutagenesis revealed an inhibitory stretch consisting of upstream nucleotides -24 to -15 that forms a long-range pairing, termed Alt 1, with the 3' strand of P2 (P2(3')) located at the very 3'-end of the ribozyme. Two other alternative pairings were found, Alt 2, which involves upstream nucleotide-ribozyme interactions, and Alt 3, which involves ribozyme-ribozyme interactions. Self-cleavage was rescued 2700 to 20,000-fold by adding DNA oligomers, which sequester the -24/-15 inhibitory stretch in trans. Surprisingly, co-transcriptional self-cleavage occurs when the number of upstream nucleotides is increased to 54. Computer prediction and structure mapping support the existence of an unusually stable upstream hairpin involving nucleotides -54 to -18, termed P(-1)/L(-1), which sequesters the majority of the -24/-15 inhibitory stretch in cis. This hairpin is followed by a stretch of single-stranded pyrimidine-rich nucleotides, termed J(-1/1). Sequence comparison suggests that the P(-1)/L(-1)/J(-1/1) motif is conserved among known genomic HDV isolates, and that the J(-1/1) stretch is conserved among antigenomic HDV isolates. Lastly, the secondary structure of the Alt 1-containing ribozyme provides insight into possible folding intermediates of the ribozyme.
Department of Chemistry, Pennsylvania State University, PA 16802, USA.
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Chadalavada
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Knudsen
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Nakano
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Bevilacqua
D000465:Algorithms; D020816:Amino Acid Motifs; D001483:Base Sequence; D017124:Conserved Sequence; D003698:Hepatitis Delta Virus / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D016337:RNA, Catalytic / Q000737:chemistry*; D012367:RNA, Viral / Q000737:chemistry*
D016337:RNA, Catalytic; D012367:RNA, Viral