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Thiobacillus ferrooxidans mer operon: sequence analysis of the promoter and adjacent genes
C Inoue1, K Sugawara, T Kusano
1Biotechnology Institute, Akita Prefectural College of Agriculture, Japan.
Abstract:
The merA upstream nucleotide (nt) sequence (1378 bp) of the Hg2(+)-resistance-encoding gene system (mer) in Thiobacillus ferrooxidans, was determined. The region contains two open reading frames: unidentified reading frame 1 (URF1) and merC. URF1 has 63-73% homology with those of Tn501, R100 and pDU1358, although the corresponding product has not yet been identified. Thiobacillus merC had 61% and 55% homology with R100 merC at the nt and amino acid (aa) sequence levels, respectively, and its product, consisting of 143 aa, was highly hydrophobic. No sequence homologous to merR, merT. merP or merD of R100 were observed on either strand. Within the 70-100-bp sequence upstream from the merC start codon. there was a sequence highly homologous to the promoter of merT of other Gram- mer systems. From primer extension and Northern-blot analyses, it became clear that merC and merA were co-transcribed from this putative transcription start point. The mer transcript in T. ferrooxidans was only detected in Hg2(+)-induced cells. Therefore, it was concluded that the T. ferrooxidans mer system is an inducible operon.
Insights
The merA gene system in Thiobacillus ferrooxidans, responsible for mercury resistance, was sequenced. Researchers found merC and an unknown gene, with merC and merA co-transcribed in an inducible operon.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The mercury resistance (mer) gene system confers resistance to heavy metals.
- Understanding the mer system in Thiobacillus ferrooxidans is crucial for bioremediation and microbial genetics.
Purpose of the Study:
- To determine the nucleotide sequence upstream of the merA gene in Thiobacillus ferrooxidans.
- To identify genes involved in mercury resistance and their regulatory mechanisms.
Main Methods:
- DNA sequencing of the merA upstream region (1378 bp).
- Analysis of open reading frames (ORFs) and sequence homology.
- Primer extension and Northern-blot analyses to determine transcription patterns.
Main Results:
- Identified two ORFs: an unidentified reading frame 1 (URF1) and merC.
- Thiobacillus merC showed significant homology to known merC sequences.
- Discovered a promoter region upstream of merC, suggesting co-transcription of merC and merA.
- The mer transcript was only detected in mercury-induced cells, indicating an inducible system.
Conclusions:
- The merA upstream region in Thiobacillus ferrooxidans contains merC and URF1.
- merC and merA are co-transcribed as part of an inducible operon regulated by mercury.
- This finding contributes to understanding mercury resistance mechanisms in bacteria.