Previous studies have indicated that in all land plants examined to date, the chloroplast gene trnLUAA isinterrupted by a single group I intron ranging from 250 to over 1400 bp. The parasitic Epifagus virginiana haslost, however, the entire gene. We report that the intron is missing from the chloroplast genome of twoarctic species of the legume genus Hedysarum (H. alpinum, H. ...

Group I introns are highly dynamic and mobile, featuring extensive presence-absence variation and widespread horizontal transfer. Group I introns can invade intron-lacking alleles via intron homing powered by their own encoded homing endonuclease gene (HEG) after horizontal transfer or via reverse splicing through an RNA intermediate. After successful invasion, the intron and HEG are subject to...

The yeast mitochondrial protein Suv3p is a putative NTP-dependent RNA helicase. Here we report that in cells lacking Suv3p, there is an approximately 50-fold increase in the excised form of the group I intron omega of the mitochondrial 31S rRNA gene. Surprisingly, little mature 21S rRNA accumulates in those cells; instead, unligated 21S rRNA exons appear. Intron overaccumulation could lead to s...

All Group I intron ribozymes contain a conserved core region consisting of two helical domains, P4-P6 and P3-P7. Recent studies have demonstrated that the elements required for catalysis are concentrated in the P3-P7 domain. We carried out in vitro selection experiments by using three newly constructed libraries on a variant of the T4 td Group I ribozyme containing only a P3-P7 domain in its co...

We have created a database of comparatively derived group I intron secondary structure diagrams. This collection currently contains a broad sampling of phylogenetically and structurally similar and diverse structures from over 200 publicly available intron sequences. As more group I introns are sequenced and added to the database, we anticipate minor refinements in these secondary structure dia...

We report the occurrence of a group I intron, 452 nucleotides in length, in the nuclear small-subunit ribosomal gene of the benthic seaweed Urospora penicilliformis, a member of the green algal class Ulvophyceae. Group I introns have been reported in fungi, myxomycetes, the ciliate genus Tetrahymena, and recently in five unicellular chlorophycean algae. The sequence of the conserved core of the...

The mtDNA rnl-U7 region has been examined for the presence of introns in selected species of the genus Ceratocystis. Comparative sequence analysis identified group I and group II introns encoding single and double motif LAGLIDADG open reading frames (ORFs) at the following positions L1671, L1787, and L1923. In addition downstream of the rnl-U7 region group I introns were detected at positions L...

Group I introns are mobile, self-splicing genetic elements found principally in organellar genomes and nuclear rRNA genes. The only group I intron known from mitochondrial genomes of vascular plants is located in the cox1 gene of Peperomia, where it is thought to have been recently acquired by lateral transfer from a fungal donor. Southern-blot surveys of 335 diverse genera of land plants now s...

Mobile group I introns are hypothesized to have arisen after invasion by endonuclease-encoding open reading frames (ORFs), which mediate their mobility. Consistent with an endonuclease-ORF invasion event, we report similarity between exon junction sequences (the recognition site for the mobility endonuclease) and intron sequences flanking the endonuclease ORF in the sunY gene of phage T4. Furth...