engleski

Transcription-associated RecA-independent homologous recombination between direct repeats in Agrobacterium tumefaciens

In the genome of many organisms, deletions arise between direct repeats due to intramolecular recombination. The frequency of recombination is affected by the length of the repeats and the distance between them. Our study, carried out in Agrobacterium tumefaciens, was based on plasmid-born recombination constructs derived from three different plant LTR-retrotransposons (Tto1, Tpv2 and Tnt1). LTR-retrotransposons are a family of mobile genetic elements, structurally related to retroviruses. The coding region of LTR-retrotransposons is flanked by long direct repeat sequences (LTRs). Although in all three retrotransposons both the distance between the repeats and the length of the repeats were similar, significantly higher frequency of deletions between LTRs was detected in Tto1. The same results were obtained in A. tumefaciens UIA143 (recA- strain). According to current models for recA-independent recombination between direct repeats in plasmid a similar rate of deletion could be expected in all three constructs. To investigate this discrepancy, transcription of the LTR-retrotransposons in A. tumefaciens has been analysed. It appeared that, in contrast to the other two retrotransposons, Tto1 was transcriptionally active. Although no direct connection between transcription and recombination has been investigated in our study, transcription-associated recombination between direct repeats has been documented in E. coli and yeast. Therefore we assume that transcription of the Tto1 might be responsible for high frequency of recombination between LTRs.

Transcription; RecA; Homologous recombination; Direct repeats; Agrobacterium tumefaciens

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