Background This laboratory has been working on fit genes (<Emphasis Type="BoldItalicUnderline">f</Emphasis>actor <Emphasis Type="BoldItalicUnderline">i</Emphasis>nvolved in <Emphasis Type="BoldItalicUnderline">t</Emphasis>ranscription) for many years. The fitA76 is temperature-sensitive (Ts) double mutant, carrying two lesions, pheS5 (pheS) and fit95 (pheT) with a combined defect at transcription. The fitB and fitC mutations were isolated as extragenic-suppressor(s) of fitA76. While fitA76 mapped at 38.7 min, fitC4 mapped at 39.01 min. The fitC4 and fitA76, were two accompanied mutations found in temperature-insensitive derivative (JV4), isolated from fitA76 mutant. The fitC4 suppresses fitA76(but not fitA76) and both are transcription defective. This work focuses on elucidating gene-identity of fitC4 locus, and its role in allele-specific genetic-suppression and genome-integrity. Methods Mutations were mobilized by P1-transductions. Marker-rescue analyses were done with Kohara-phages to narrow down the fitC4 location. Further mapping was done by complementation analyses employing various plasmids spanning that region. Complementation assays were quantitated by relative viability. Results Among the Kohara phages/clones tested (321–330), the same clones 322&323 which earlier marker rescued fitA76/fit95 mutations, also marker rescued fitC4 mutation. But, fitC4 maps totally outside the overlapping region of two Kohara phages, tested positive. Complementation analyses by various plasmids spanning that region indicate that, fitC4 is same as pheS. Further, one of the clones bearing only pheT+, did not complement fitC4 mutation. The implications of these results and pheST operon dynamics in gene duplication towards bacterial adaptation in context of transcription regulation and genome expansion are discussed. Conclusion The fitC4 is same as pheS allele. Only pheS but not full pheST-operon is duplicated as fitC4. The pheS gene duplication could help in allele-specific genetic suppression and adaptation of its ability as transcription factor, thus contributing to genome-stability and genome-evolution.

pheST operon dynamics and pheS gene duplication mediated genome stability and evolution in E. coli: evidence that fitC4 is an allele of pheS

期刊论文
发表日期：

2025年6月4日

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Praveen Belagal

摘要

Background

This laboratory has been working on fit genes (factor involved in transcription) for many years. The fitA76 is temperature-sensitive (Ts) double mutant, carrying two lesions, pheS5 (pheS) and fit95 (pheT) with a combined defect at transcription. The fitB and fitC mutations were isolated as extragenic-suppressor(s) of fitA76. While fitA76 mapped at 38.7 min, fitC4 mapped at 39.01 min. The fitC4 and fitA76*, were two accompanied mutations found in temperature-insensitive derivative (JV4), isolated from fitA76 mutant. The fitC4 suppresses fitA76*(but not fitA76) and both are transcription defective. This work focuses on elucidating gene-identity of fitC4 locus, and its role in allele-specific genetic-suppression and genome-integrity.

Methods

Mutations were mobilized by P1-transductions. Marker-rescue analyses were done with Kohara-phages to narrow down the fitC4 location. Further mapping was done by complementation analyses employing various plasmids spanning that region. Complementation assays were quantitated by relative viability.

Results

Among the Kohara phages/clones tested (321–330), the same clones 322&323 which earlier marker rescued fitA76/fit95 mutations, also marker rescued fitC4 mutation. But, fitC4 maps totally outside the overlapping region of two Kohara phages, tested positive. Complementation analyses by various plasmids spanning that region indicate that, fitC4 is same as pheS. Further, one of the clones bearing only pheT⁺, did not complement fitC4 mutation. The implications of these results and pheST operon dynamics in gene duplication towards bacterial adaptation in context of transcription regulation and genome expansion are discussed.

Conclusion

The fitC4 is same as pheS allele. Only pheS but not full pheST-operon is duplicated as fitC4. The pheS gene duplication could help in allele-specific genetic suppression and adaptation of its ability as transcription factor, thus contributing to genome-stability and genome-evolution.