Structure and evolution of myxomycete nuclear group I introns: a model for horizontal transfer by intron homing

1992 ◽  
Vol 22 (4) ◽  
pp. 297-304 ◽  
Author(s):  
Steinar Johansen ◽  
Terje Johansen ◽  
Finn Haugli
Keyword(s):  
Horizontal Transfer ◽  
Group I Introns ◽  
Group I ◽  
Intron Homing ◽  
Nuclear Group

scholarly journals Nuclear group I introns in self-splicing and beyond

Mobile DNA ◽  
2013 ◽  
Vol 4 (1) ◽  
pp. 17 ◽  
Author(s):  
Annica Hedberg ◽  
Steinar D Johansen
Keyword(s):  
Group I Introns ◽  
Group I ◽  
Self Splicing ◽  
Nuclear Group

scholarly journals A Phylogenetic Approach to Structural Variation in Organization of Nuclear Group I Introns and Their Ribozymes

2021 ◽  
Vol 7 (3) ◽  
pp. 43
Author(s):  
Betty M. N. Furulund ◽  
Bård O. Karlsen ◽  
Igor Babiak ◽  
Steinar D. Johansen
Keyword(s):  
Binding Site ◽  
Ribosomal Dna ◽  
Homing Endonuclease ◽  
Direct Repeat ◽  
Small Subunit ◽  
Sequence Motif ◽  
Group I Introns ◽  
Group I ◽  
Eukaryotic Microorganisms ◽  
Nuclear Group

Nuclear group I introns are restricted to the ribosomal DNA locus where they interrupt genes for small subunit and large subunit ribosomal RNAs at conserved sites in some eukaryotic microorganisms. Here, the myxomycete protists are a frequent source of nuclear group I introns due to their unique life strategy and a billion years of separate evolution. The ribosomal DNA of the myxomycete Mucilago crustacea was investigated and found to contain seven group I introns, including a direct repeat-containing intron at insertion site S1389 in the small subunit ribosomal RNA gene. We collected, analyzed, and compared 72 S1389 group IC1 introns representing diverse myxomycete taxa. The consensus secondary structure revealed a conserved ribozyme core, but with surprising sequence variations in the guanosine binding site in segment P7. Some S1389 introns harbored large extension sequences in the peripheral region of segment P9 containing direct repeat arrays. These repeats contained up to 52 copies of a putative internal guide sequence motif. Other S1389 introns harbored homing endonuclease genes in segment P1 encoding His-Cys proteins. Homing endonuclease genes were further interrupted by small spliceosomal introns that have to be removed in order to generate the open reading frames. Phylogenetic analyses of S1389 intron and host gene indicated both vertical and horizontal intron transfer during evolution, and revealed sporadic appearances of direct repeats, homing endonuclease genes, and guanosine binding site variants among the myxomycete taxa.

Homology Requirements for Double-Strand Break-Mediated Recombination in a Phage λ-td Intron Model System

Genetics ◽  
1996 ◽  
Vol 143 (3) ◽  
pp. 1057-1068 ◽  
Author(s):  
Monica M Parker ◽  
Deborah A Court ◽  
Karen Preiter ◽  
Marlene Belfort
Keyword(s):  
Strand Break ◽  
Double Strand Break ◽  
Model System ◽  
Group I Introns ◽  
Wild Type ◽  
Intron Insertion ◽  
Homologous Recombination Event ◽  
Group I ◽  
Intron Homing

Abstract Many group I introns encode endonucleases that promote intron homing by initiating a double-strand break-mediated homologous recombination event. A td intron-phage λ model system was developed to analyze exon homology effects on intron homing and determine the role of the λ 5′–3′ exonuclease complex (Redαβ) in the repair event. Efficient intron homing depended on exon lengths in the 35- to 50-bp range, although homing levels remained significantly elevated above nonbreak-mediated recombination with as little as 10 bp of flanking homology. Although precise intron insertion was demonstrated with extremely limiting exon homology, the complete absence of one exon produced illegitimate events on the side of heterology. Interestingly, intron inheritance was unaffected by the presence of extensive heterology at the double-strand break in wild-type λ, provided that sufficient homology between donor and recipient was present distal to the heterologous sequences. However, these events involving heterologous ends were absolutely dependent on an intact Red exonuclease system. Together these results indicate that heterologous sequences can participate in double-strand break-mediated repair and imply that intron transposition to heteroallelic sites might occur at break sites within regions of limited or no homology.

Reverse splicing of a mobile twin-ribozyme group I intron into the natural small subunit rRNA insertion site

2005 ◽  
Vol 33 (3) ◽  
pp. 482-484 ◽  
Author(s):  
Å.B. Birgisdottir ◽  
S.D. Johansen
Keyword(s):  
Horizontal Transfer ◽  
Homing Endonuclease ◽  
Insertion Site ◽  
Group I Intron ◽  
Small Subunit ◽  
Group I Introns ◽  
Small Subunit Rrna ◽  
Homing Endonuclease Gene ◽  
Group I ◽  
Endonuclease Gene

A mobile group I intron containing two ribozyme domains and a homing endonuclease gene (twin-ribozyme intron organization) can integrate by reverse splicing into the small subunit rRNA of bacteria and yeast. The integration is sequence-specific and corresponds to the natural insertion site (homing site) of the intron. The reverse splicing is independent of the homing endonuclease gene, but is dependent on the group I splicing ribozyme domain. The observed distribution of group I introns in nature can be explained by horizontal transfer between natural homing sites by reverse splicing and subsequent spread in populations by endonuclease-dependent homing.

scholarly journals Group I Intron Homing in Bacillus Phages SPO1 and SP82: a Gene Conversion Event Initiated by a Nicking Homing Endonuclease

2004 ◽  
Vol 186 (13) ◽  
pp. 4307-4314 ◽  
Author(s):  
Markus Landthaler ◽  
Nelson C. Lau ◽  
David. A. Shub
Keyword(s):  
Gene Conversion ◽  
Recombination Event ◽  
Homing Endonuclease ◽  
Gene Conversion Event ◽  
Group I Introns ◽  
Conversion Event ◽  
Homologous Recombination Event ◽  
Group I ◽  
Intron Homing

ABSTRACT Many group I introns encode endonucleases that promote intron homing by initiating a double-stranded break-mediated homologous recombination event. In this work we describe intron homing in Bacillus subtilis phages SPO1 and SP82. The introns encode the DNA endonucleases I-HmuI and I-HmuII, respectively, which belong to the H-N-H endonuclease family and possess nicking activity in vitro. Coinfections of B. subtilis with intron-minus and intron-plus phages indicate that I-HmuI and I-HmuII are required for homing of the SPO1 and SP82 introns, respectively. The homing process is a gene conversion event that does not require the major B. subtilis recombination pathways, suggesting that the necessary functions are provided by phage-encoded factors. Our results provide the first examples of H-N-H endonuclease-mediated intron homing and the first demonstration of intron homing initiated by a nicking endonuclease.

scholarly journals The Mitochondrial Genome of the Sea Anemone Stichodactyla haddoni Reveals Catalytic Introns, Insertion-Like Element, and Unexpected Phylogeny

Life ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 402
Author(s):  
Steinar Daae Johansen ◽  
Sylvia I. Chi ◽  
Arseny Dubin ◽  
Tor Erik Jørgensen
Keyword(s):  
Phylogenetic Analyses ◽  
Homing Endonuclease ◽  
Mitochondrial Genes ◽  
Sea Anemone ◽  
Group I Introns ◽  
Sea Anemones ◽  
Group I ◽  
Genes Encoding ◽  
Intron Homing ◽  
Stichodactyla Haddoni

A hallmark of sea anemone mitochondrial genomes (mitogenomes) is the presence of complex catalytic group I introns. Here, we report the complete mitogenome and corresponding transcriptome of the carpet sea anemone Stichodactyla haddoni (family Stichodactylidae). The mitogenome is vertebrate-like in size, organization, and gene content. Two mitochondrial genes encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI) are interrupted with complex group I introns, and one of the introns (ND5-717) harbors two conventional mitochondrial genes (ND1 and ND3) within its sequence. All the mitochondrial genes, including the group I introns, are expressed at the RNA level. Nonconventional and optional mitochondrial genes are present in the mitogenome of S. haddoni. One of these gene codes for a COI-884 intron homing endonuclease and is organized in-frame with the upstream COI exon. The insertion-like orfA is expressed as RNA and translocated in the mitogenome as compared with other sea anemones. Phylogenetic analyses based on complete nucleotide and derived protein sequences indicate that S. haddoni is embedded within the family Actiniidae, a finding that challenges current taxonomy.

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