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Mol. Cell. Biol., 05 1995, 2828-2838, Vol 15, No. 5
JV Moran, S Zimmerly, R Eskes, JC Kennell, AM Lambowitz, RA Butow and PS Perlman
Group II introns aI1 and aI2 of the yeast mitochondrial COXI gene are
mobile elements that encode an intron-specific reverse transcriptase (RT)
activity. We show here that the introns of Saccharomyces cerevisiae
ID41-6/161 insert site specifically into intronless alleles. The mobility
is accompanied by efficient, but highly asymmetric, coconversion of nearby
flanking exon sequences. Analysis of mutants shows that the aI2 protein is
required for the mobility of both aI1 and aI2. 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. Surprisingly, there
appear to be two mobility modes: the major one involves cDNAs reverse
transcribed from unspliced precursor RNA; the minor one, observed in two
mutants lacking detectable RT activity, appears to involve DNA level
recombination. A cis-dominant splicing-defective mutant of aI2 continues to
synthesize cDNAs containing the introns but is completely defective in both
mobility modes, indicating that the splicing or the structure of the intron
is required. Our results demonstrate that the yeast group II intron aI2 is
a retroelement that uses novel mobility mechanisms.
Copyright © 1995, American Society for Microbiology
Mobile group II introns of yeast mitochondrial DNA are novel site- specific retroelements
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235-9038, USA.
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