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Characterization of the umu-complementing operon from R391
O I Kulaeva1, J C Wootton, A S Levine
1Section on DNA Replication, Repair and Mutagenesis, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892-2725, USA.
Journal of Bacteriology
|May 1, 1995
Summary
New plasmid genes, rumAB(R391), aid mutagenic DNA repair, similar to chromosomal umuDC genes. These genes represent a new subfamily and show unique regulation and protein processing, impacting mutagenesis levels.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- R factors, plasmids conferring antibiotic and heavy metal resistance, can carry genes for mutagenic DNA repair.
- These plasmid-encoded genes are homologous to chromosomally encoded umuDC genes found in bacteria like Escherichia coli and Salmonella typhimurium.
- Previous studies characterized plasmid operons mucAB, impCAB, and samAB involved in DNA repair.
Purpose of the Study:
- To molecularly characterize the umu-complementing operon from the IncJ plasmid R391.
- To analyze the genetic and phylogenetic relationship of the R391 operon to known umuDC and other plasmid-borne umu-like genes.
- To investigate the functional characteristics and regulation of the R391 operon in bacterial mutagenesis.
Main Methods:
- Nucleotide sequencing of the minimal R plasmid umu-complementing (rum) region.
- Phylogenetic analysis of the deduced RumAB(R391) protein sequences.
- Genetic characterization of the rumAB(R391) operon in different recA genetic backgrounds.
- Assessment of mutagenesis levels and protein processing in recA mutant strains.
Main Results:
- The rum region contains a two-gene operon, rumA(R391) and rumB(R391), with a LexA-binding-like regulatory site.
- Phylogenetic analysis places RumAB(R391) proteins as a new subfamily, distinct from chromosomal UmuDC and other plasmid Umu-like proteins.
- The rumAB(R391) operon exhibited phenotypes similar to mucAB in recA+ and recA1730 strains but intermediate mutagenesis in recA430 strains.
- This intermediate mutagenesis correlated with reduced posttranslational processing of RumA(R391) to its active form, RumA'(R391).
Conclusions:
- The rumAB(R391) operon represents a novel subfamily of plasmid-encoded umu-like genes involved in mutagenic DNA repair.
- Its regulatory and functional characteristics share similarities with both chromosomal umuDC and other plasmid-encoded umu-like operons.
- The operon's unique protein processing mechanism influences its mutagenic potential, highlighting the diversity of DNA repair mechanisms encoded by plasmids.