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Complete nucleotide sequence and characterization of pUA140, a cryptic plasmid from Streptococcus mutans
1Department of Oral Biology, School of Dentistry, University of Alabama at Birmingham, AL 35294, USA.
Abstract:
Approximately 5% of strains of Streptococcus mutans contain plasmid DNA. Strain UA140 harbors a 5.6-kb cryptic plasmid, pUA140, with an overall G+C content of 32.7%. Five open reading frames (ORF), encoding peptides of larger than 100 amino acid residues, were initially designated as ORF1 to ORF5. These five ORFs were located on the same strand of pUA140. ORF1 (258 amino acids) resembled a replication protein, Rep. Upstream of the putative Rep gene, a double-stranded origin for plasmid replication that showed strong similarity to those of a number of plasmids in the pT181 family was identified. Further upstream was a region constituting the single-stranded origin of replication. A single-stranded DNA intermediate was detected during plasmid replication. Taken together, these results suggest that pUA140 replicated by the rolling circle replication mechanism but exhibited several characteristics that differ from those of other members of the pT181 plasmid family.
Insights
Streptococcus mutans strain UA140 contains a cryptic plasmid, pUA140, that replicates via rolling circle mechanism. This plasmid shows unique characteristics differentiating it from the pT181 family.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus mutans is a key pathogen in dental caries.
- Plasmid DNA is found in approximately 5% of S. mutans strains.
- Understanding plasmid replication mechanisms is crucial for microbial genetics.
Purpose of the Study:
- To characterize the cryptic plasmid pUA140 from Streptococcus mutans strain UA140.
- To elucidate the replication mechanism of pUA140.
- To compare pUA140 with other known plasmid families.
Main Methods:
- Plasmid DNA isolation and characterization.
- Open reading frame (ORF) identification and analysis.
- Sequence homology searches and replication origin identification.
- Detection of single-stranded DNA intermediates.
Main Results:
- pUA140 is a 5.6-kb cryptic plasmid with a G+C content of 32.7%.
- Five ORFs were identified, with ORF1 showing similarity to a replication protein (Rep).
- pUA140 possesses double-stranded and single-stranded origins of replication, characteristic of rolling circle replication.
- A single-stranded DNA intermediate was detected, confirming rolling circle replication.
Conclusions:
- pUA140 replicates via the rolling circle mechanism.
- pUA140 exhibits distinct features compared to other pT181 family plasmids.
- Further research is needed to fully understand the unique aspects of pUA140 replication.