The ability to form full-length intron RNA circles is a general property of nuclear group I introns.
In addition to splicing, group I intron RNA is capable of an alternative two-step processing pathway that results in the formation of full-length intron circular RNA. The circularization pathway is initiated by hydrolytic cleavage at the 3' splice site and followed by a transesterification reaction in which the intron terminal guanosine attacks the 5' splice site presented in a structure analogous to that of the first step of splicing. The products of the reactions are full-length circular intron and unligated exons. For this reason, the circularization reaction is to the benefit of the intron at the expense of the host. The circularization pathway has distinct structural requirements that differ from those of splicing and appears to be specifically suppressed in vivo. The ability to form full-length circles is found in all types of nuclear group I introns, including those from the Tetrahymena ribosomal DNA. The biological function of the full-length circles is not known, but the fact that the circles contain the entire genetic information of the intron suggests a role in intron mobility.
Nielsen
Henrik
H
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark.
Fiskaa
Tonje
T
Birgisdottir
Asa Birna
AB
Haugen
Peik
P
Einvik
Christer
C
Johansen
Steinar
S
D001483:Base Sequence; D002467:Cell Nucleus / Q000737:chemistry*; D017931:DNA Primers; D005091:Exons; D006868:Hydrolysis; D007438:Introns; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry* / Q000235:genetics; D012322:RNA Precursors / Q000737:chemistry; D012326:RNA Splicing; D000079962:RNA, Circular
D017931:DNA Primers; D012322:RNA Precursors; D000079962:RNA, Circular; D012313:RNA