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Recombination enhancement by replication (RER) in Rhizobium etli
1Programa de Genética Molecular de Plásmidos Bacterianos, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, 62210 Cuernavaca, Morelos, México.
Genetics
|April 11, 2000
Summary
Replication can significantly increase recombination. In Rhizobium etli, inducing theta-type replication on the symbiotic plasmid caused a 1000-fold rise in deletions, a process termed recombination enhancement by replication (RER).
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Recombination and replication are closely intertwined processes in all organisms.
- Replication can induce recombination, with varying effects depending on the replication mechanism (e.g., rolling circle vs. theta-type).
- Theta-type replication typically causes only a modest increase in recombination frequency.
Purpose of the Study:
- To investigate the impact of inducing theta-type replication from an additional origin on the symbiotic plasmid (pSym) of Rhizobium etli.
- To characterize the phenomenon of recombination enhancement by replication (RER) in this bacterial system.
Main Methods:
- Induction of theta-type replication from a supernumerary origin in the pSym of Rhizobium etli.
- Analysis of deletion formation, spanning the symbiotic region, with endpoints at reiterated nitrogenase operons.
- Assessment of RER dependency on factors like replication origin position, fork direction, distance to repeats, and the recA allele.
Main Results:
- Induction of theta-type replication resulted in a 1000-fold increase in deletion formation on the pSym.
- These deletions specifically targeted the symbiotic region and were flanked by nitrogenase operons.
- RER was independent of replication origin location, fork direction, or distance to repeats, but crucially dependent on an active recA allele, indicating homologous recombination.
Conclusions:
- Recombination enhancement by replication (RER) is a significant phenomenon in Rhizobium etli, driven by homologous recombination.
- RER is a region-specific process, concentrated within the symbiotic region of the pSym.
- The findings offer insights into the interplay between replication and recombination, with potential parallels to chromosomal recombination at replication termini.