title: The group I-like ribozyme DiGIR1 mediates alternative processing of pre-rRNA transcripts in Didymium iridis.
abstract: During starvation induced encystment, cells of the myxomycete 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 twin-ribozyme 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 lacking its two group I introns. The formation of this RNA implies cleavage by DiGIR1 in a new RNA context, and presents a new example of the cost to the host of intron load. This is because the formation of the 7.5-kb RNA is incompatible with the formation of functional ribosomal RNA from 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 rRNA and I-DirI mRNA in growing cells, suggesting an interplay between the two ribozymes of a twin-ribozyme intron.
authors.affiliation: Department of Medical Biochemistry and Genetics, The Panum Institute, Copenhagen, Denmark.
authors.forename: Anna
authors.initials: A
authors.lastname: Vader
authors.forename: Steinar
authors.initials: S
authors.lastname: Johansen
authors.forename: Henrik
authors.initials: H
authors.lastname: Nielsen
mesh_terms: D017398:Alternative Splicing; D001483:Base Sequence; D002384:Catalysis; D017931:DNA Primers; D007438:Introns; D009235:Myxomycetes / Q000201:enzymology / Q000235:genetics*; D012322:RNA Precursors / Q000235:genetics*; D016337:RNA, Catalytic / Q000235:genetics* / Q000378:metabolism; D012331:RNA, Fungal / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics*
chemical_list: D017931:DNA Primers; C116167:GIR1 ribozyme; D012322:RNA Precursors; D016337:RNA, Catalytic; D012331:RNA, Fungal; D012335:RNA, Ribosomal