Transcriptional regulation of the protocatechuate 4,5-cleavage pathway genes in Sphingomonas paucimobilis SYK-6 by LigR, a LysR-type transcriptional regulator

点击翻译按钮获取中文摘要

The protocatechuate (PCA) 4,5-cleavage pathway is the essential metabolic route for lignin catabolism in Sphingomonas paucimobilis SYK-6. Here, we examined the operon structure of the PCA 4,5-cleavage pathway genes and investigated the transcriptional regulation of the genes. Reverse transcription-PCR analysis indicated that the PCA 4,5-cleavage pathway genes of SYK-6 consist of three transcriptional units, including the ligK-orf1-ligI-lsdA operon, the ligJ-ligA-ligB-ligC operon, and the monocistronic ligR. In the presence of PCA, transcription of the ligK and ligJ operons was induced 10-to 40-fold in SYK-6, however, this induction was no longer observed in the ligR mutant. Inducible transcription of these operons was not influenced by the disruption of ligB, which encodes a large subunit of PCA 4,5-dioxygenase. This result strongly suggested that PCA acts as an inducer of these operons. The promoter regions of these operons were determined by the promoter-lacZ transcriptional fusion analysis. Gel retardation assay exhibited the specific DNA binding of LigR to the promoter regions of ligK and ligJ operons. In conclusion, the PCA 4,5-cleavage pathway genes of SYK-6 consist of three transcriptional units. Transcriptions from the ligK and ligJ promoters are directly up-regulated by LigR, and transcription of these operons requires PCA as an inducer.