Multiple Homing Pathways Used by Yeast Mitochondrial Group II Introns
| Autor: | Michael Y. Chao, Philip S. Perlman, Lorna Dickson, Robert Eskes, Lu Liu, Alan M. Lambowitz, Hongwen Ma |
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| Jazyk: | angličtina |
| Rok vydání: | 2000 |
| Předmět: |
DNA
Complementary DNA Repair Retroelements DNA repair Molecular Sequence Data Biology Exon chemistry.chemical_compound Yeasts Molecular Biology Crosses Genetic Genetics Recombination Genetic Base Sequence Intron RNA-Directed DNA Polymerase Cell Biology Group II intron Exons Endonucleases DNA Dynamics and Chromosome Structure Introns Mitochondria Sense strand chemistry RNA splicing Mutation Homologous recombination DNA |
| Popis: | The yeast mitochondrial DNA group II introns aI1 and aI2 are retroelements that insert site specifically into intronless alleles by a process called homing. 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. All three pathways are initiated by cleavage of the recipient DNA target site by the intron-encoded endonuclease, with the sense strand cleaved by partial or complete reverse splicing, and the antisense strand cleaved by the intron-encoded protein. The major retrohoming pathway in standard crosses leads to insertion of the intron with unidirectional coconversion of upstream exon sequences. This pattern of coconversion suggests that the major retrohoming pathway is initiated by target DNA-primed reverse transcription of the reverse-spliced intron RNA and completed by double-strand break repair (DSBR) recombination with the donor allele. The RT-independent pathway leads to insertion of the intron with bidirectional coconversion and presumably occurs by a conventional DSBR recombination mechanism initiated by cleavage of the recipient DNA target site by the intron-encoded endonuclease, as for group I intron homing. Finally, some mutant DNA target sites shift up to 43% of retrohoming to another pathway not previously detected for aI2 in which there is no coconversion of flanking exon sequences. This new pathway presumably involves synthesis of a full-length cDNA copy of the inserted intron RNA, with completion by a repair process independent of homologous recombination, as found for the Lactococcus lactis Ll.LtrB intron. Our results show that group II intron mobility can occur by multiple pathways, the ratios of which depend on the characteristics of both the intron and the DNA target site. This remarkable flexibility enables group II introns to use different recombination and repair enzymes in different host cells. |
| Databáze: | OpenAIRE |
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