Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The sporadic distribution of nuclear group I introns among different fungal lineages can be explained by vertical inheritance of the introns followed by successive losses, or horizontal transfers from one lineage to another through intron homing or reverse splicing. Homing is mediated by an intron-encoded homing endonuclease (HE) and recent studies suggest that the introns and their associated HE gene (HEG) follow a recurrent cyclical model of invasion, degeneration, loss, and reinvasion. The purpose of this study was to compare this model to the evolution of HEGs found in the group I intron at position S943 of the nuclear ribosomal DNA of the lichen-forming fungus Pleopsidium. Forty-eight S943 introns were found in the 64 Pleopsidium samples from a worldwide screen, 22 of which contained a full-length HEG that encodes a putative 256-amino acid HE, and 2 contained HE pseudogenes. The HEGs are divided into two closely related types (as are the introns that encode them) that differ by 22.6% in their nucleotide sequences. The evolution of the Pleopsidium intron-HEG element shows strong evidence for a cyclical model of evolution. The intron was likely acquired twice in the genus and then transmitted via two or three interspecific horizontal transfers. Close geographical proximity plays an important role in intron-HEG horizontal transfer because most of these mobile elements were found in Europe. Once acquired in a lineage, the intron-HEG element was also vertically transmitted, and occasionally degenerated or was lost.
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PMID:Evolution of Pleopsidium (lichenized Ascomycota) S943 group I introns and the phylogeography of an intron-encoded putative homing endonuclease. 1729 23

The chloroplast-encoded large subunit ribosomal RNA gene of several free-living green algae contains group I introns at Escherichia coli genic positions 1917, 1931, 1951, and 2449. Herein we report the presence of group I introns at these positions within the chloroplast-encoded large subunit ribosomal RNA gene of several lichen-forming green algae belonging to the Trebouxia genus. In contrast to the introns inserted at position 2449, all introns inserted at positions 1917, 1931, and 1951 contained LAGLIDADG homing endonuclease genes. Phylogenetic analyses show that: (i) introns inserted at positions 1917, 1931, and 1951 are closely related to introns located at homologous insertion sites in bacterial rDNA genes; and (ii) introns inserted at position 2449 are closely related to fungal introns located at homologous insertion sites in mitochondrial rDNA genes. The symbiogenetic thalli of some lichens are proposed as the likely setting of horizontal transfer of genetic material among distantly related organisms such as bacteria, fungi, and green algae.
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PMID:Presence of multiple group I introns closely related to bacteria and fungi in plastid 23S rRNAs of lichen-forming Trebouxia. 1944 Sep 84