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Báo cáo Y học: The group I-like ribozyme DiGIR1 mediates alternative processing of pre-rRNA transcripts in Didymium iridis

During starvation induced encystment, cells of the myxo-myceteDidymiumiridisaccumulate a7.5-kbRNAthat is the result of alternative processing of pre-rRNA. The 5¢ end corresponds to an internal processing site cleaved by the group I-like ribozyme DiGIR1, located within the twin-ribozyme intron Dir.S956-1. The RNAretains the majority ofDir.S956-1 including thehoming endonuclease geneanda small spliceosomal intron, the internal transcribed spacers ITS1 and ITS2, and the large subunit rRNAlacking its two group I introns. . | Eur. J. Biochem. 269 5804-5812 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.03283.x The group I-like ribozyme DiGIRI mediates alternative processing of pre-rRNA transcripts in Didymium iridis Anna Vader1 2 Steinar Johansen2 and Henrik Nielsen1 1 Department of Medical Biochemistry and Genetics The Panum Institute Copenhagen Denmark department of Molecular Biotechnology Institute of Medical Biology University of Troms0 Norway During starvation induced encystment cells of the myxo-mycete Didymium iridis accumulate a 7.5-kb RNA that is the result of alternative processing of pre-rRNA. The 5 end corresponds to an internal processing site cleaved by the group I-like ribozyme DiGIR1 located within the twinribozyme intron Dir.S956-1. The RNA retains the majority of Dir.S956-1 including the homing endonuclease gene and a small spliceosomal intron the internal transcribed spacers ITS1 and ITS2 and the large subunit rRNA atckíng íss two group I introns. The formation of this RNAimplies cleavage by DiGIR1 in a new RNA con tex t and presen ts a new example of the cost to the host of intron load. This is because the formation of the 7.5-kb RNA ÍS incompatíbte with the formation of functional ribosomal RNAfrom the same transcript. In the formation of the 7.5-kb RNA DiGIR1 catalysed cleavage takes place without prior splicing performed by DiGIR2. This contrasts with the processing order leading to mature rRNAand I- DirI mRNAin growing cells suggesting an interplay between the two ribozymes of a twinribozyme intron. Keywords Didymium iridis group I intron ribozyme pre-rRNAprocessing. Group I introns contain a conserved set of sequences and structural elements that are involved in the removal of the intron by splicing. They constitute one class out of fewer than 10 classes of naturally occurring ribozymes 1 . Group I introns vary considerably in complexity. Most introns contain only the sequence information required for splicing whereas others contain large extensions of the .