Novel heat shock response mechanism mediated by the initiation nucleotide of transcription

[摘要] Among SigA-dependent promoters in Bacillussubtilis, we compared the nucleotide sequences ofheat shock responding and non-responding promoters. Chimeric promoter experiments revealed thatthe heat shock response could be ascribed to theinitiation nucleotide (iNTP) of the transcription.Our in vivo reporter assay results indicated that afull response was achieved using GTP, a reducedresponse was observed using ATP, and no additionalexpression was observed using UTP or CTP.We then investigated the in vitro transcription assayin more detail. Enhanced transcription that wasdependent upon the iNTP was observed when heattreatment was administered during the pre-initiation period. We next analyzed the efficiency of opencomplex formation using potassium permanganatefootprinting, and our results revealed an increasein the ratio of open complex formation at elevatedtemperatures. Based on this, we suggest that theoverall intensification of transcription at high temperatures was derived from the high efficiency ofopen complex formation together with the highaffinity of RNA polymerase (RNAP) for the initiationnucleotide GTP.To determine if this mechanism observed inB. subtilis RNAP is common among bacterial species, we performed similar experiments usingEscherichia coli RNAP. Our results indicated thatE. coli RNAP also exhibited both temperature- andiNTP-dependent enhancement of transcription.Although the temperature ranges and the ratios ofenhancement are somewhat different, the overallheat shock response mechanism mediated by theiNTP of transcription appears to be conservedamong bacterial RNAP.

[学科分类] 微生物学和免疫学

[关键词] heat shock response;Bacillus subtilis;transcription;initiation nucleotide