High impact information on AI2

• For aI2, sense-strand cleavage occurs mainly by a partial reverse splicing reaction, whereas for aI1, complete reverse splicing occurs, leading to insertion of the linear intron RNA into double-stranded DNA [1].
• Reverse transcription of aI2-containing pre-mRNA is primed by the antisense strand cleaved in exon 3 and results in cotransfer of the intron and flanking exon sequences [2].
• RNA isolated from yeast mitochondria also contains circles, indicating that at least one group II intron (aI2) forms circles in vivo [3].
• Here, we used patterns of flanking marker coconversion in crosses with wild-type and mutant aI2 introns to distinguish three coexisting homing pathways: two that were reverse transcriptase (RT) dependent (retrohoming) and one that was RT independent [4].
• Efficient mobility is dependent on both the RT activity of the aI2-encoded protein and a separate function, a putative DNA endonuclease, that is associated with the Zn2+ finger-like region of the intron reading frame [5].

Biological context of AI2

• Northern blot analyses of mitochondrial transcripts indicate cox24 null mutants to be blocked in processing of introns aI2 and aI3 [6].
• RNA splicing in yeast mitochondria: DNA sequence analysis of mit- mutants deficient in the excision of introns aI1 and aI2 of the gene for subunit I of cytochrome c oxidase [7].
• RNA blot analysis shows that in addition to a reduced (mutant M15-190) or blocked (mutant M12-193) excision of the mutated intron aI1, the mutants are unable to excise the adjacent aI2 intron, the reading frame of which displays an amino acid sequence similarity to aI1 [7].
• (1982), is controlled by the activity of the maturases encoded by their respective ORFs and that the translation of the aI2 maturase depends on the previous excision of aI1 IVS [8].
• Non-denaturing gel electrophoresis and activity assays show that the aI2 reverse transcriptase is associated predominantly with the excised intron RNA, while a smaller amount is associated with unspliced precursor RNA, as expected from the role of the protein in RNA splicing [9].

Other interactions of AI2

• Mitochondrial introns aI1 and/or aI2 are needed for the in vivo deletion of intervening sequences [10].

References