Related Experiment Videos
Structural elements required for replication and incompatibility of the Rhizobium etli symbiotic plasmid
M A Ramírez-Romero1, N Soberón, A Pérez-Oseguera
1Programa de Evolución Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
Abstract:
The symbiotic plasmid of Rhizobium etli CE3 belongs to the RepABC family of plasmid replicons. This family is characterized by the presence of three conserved genes, repA, repB, and repC, encoded by the same DNA strand. A long intergenic sequence (igs) between repB and repC is also conserved in all members of the plasmid family. In this paper we demonstrate that (i) the repABC genes are organized in an operon; (ii) the RepC product is essential for replication; (iii) RepA and RepB products participate in plasmid segregation and in the regulation of plasmid copy number; (iv) there are two cis-acting incompatibility regions, one located in the igs (incalpha) and the other downstream of repC (incbeta) (the former is essential for replication); and (v) RepA is a trans-acting incompatibility factor. We suggest that incalpha is a cis-acting site required for plasmid partitioning and that the origin of replication lies within incbeta.
Insights
The RepABC plasmid replication system in Rhizobium etli CE3 involves essential genes (repA, repB, repC) and regulatory regions for replication and segregation. Key findings detail the operon structure and functional roles of RepA, RepB, and RepC proteins.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- The RepABC family represents a common type of plasmid replicon found in bacteria.
- These plasmids are crucial for symbiosis, as seen in Rhizobium etli CE3.
- Conserved genes (repA, repB, repC) and an intergenic sequence (igs) are characteristic features.
Purpose of the Study:
- To elucidate the functional roles of repABC genes and associated regions in Rhizobium etli CE3 plasmid replication and maintenance.
- To characterize the genetic organization and regulatory mechanisms of the RepABC replicon.
Main Methods:
- Genetic analysis of the repABC operon and intergenic regions.
- Functional studies involving gene products (RepA, RepB, RepC) and cis-acting elements.
- Replication and incompatibility assays.
Main Results:
- Demonstrated that repABC genes are organized as an operon.
- Identified RepC as essential for replication, while RepA and RepB regulate copy number and segregation.
- Discovered two cis-acting incompatibility regions (incalpha and incbeta) and identified RepA as a trans-acting incompatibility factor.
- Located the replication origin within incbeta and proposed incalpha's role in partitioning.
Conclusions:
- The RepABC system employs a complex interplay of genes and regulatory sequences for stable plasmid inheritance.
- Understanding these mechanisms is vital for manipulating symbiotic plasmids in bacteria like Rhizobium etli.