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Report No.

Internal promoter characterization and expression of the ${it Deinococcus radiodurans pprI}$-${it folP}$ gene cluster

Gao, G.*; Le, D.*; Huang, L.*; Lu, H.*; Narumi, Issei; Hua, Y.*

PprI is a general gene switch responsible for the extraordinary radioresistance of ${it Deinococcus radiodurans}$. From NCBI DNA sequence analysis, it was predicted that the translation start codon of the downstream ${it folP}$ gene overlaps the ${it pprI}$ stop codon, suggesting that these genes may form an operon. In this study, we show that a mutant containing an inserted sequence in ${it folP}$ does not grow unless folate is added to the medium, but is not affected in extreme radioresistance, whereasa ${it pprI}$ disruptant strain could grow in absence of folate. We now characterize the promoter of ${it pprI}$ by primer extension experiments. We show that expression of a ${it pprI}$-${it lacZ}$ fusion is constitutive and unaltered following ionizing radiation as is the production of the PprI protein. PprI protein is not expressed if its promoter is deleted and the transcription from the entire ${it pprI}$ promoter (containing a large region upstream of ${it pprI}$ gene) is essential for radioresistance of ${it D. radiodurans}$. However, the deletion of ${it pprI}$ promoter has no effect on the expression of the ${it folP}$-${it lacZ}$ fusion. Primer extension analysis of the ${it folP}$ promoter region shows that ${it folP}$ is transcribed from its own promoter located within the ${it pprI}$ structural gene. All these results do neither support the existence of a ${it pprI}$-${it folP}$ operon nor a regulatory role of FolP in ${it pprI}$ expression.



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