Evolutionary analysis of prokaryotic heat-shock transcription regulatory protein σ32

Abstract

Heat-stress to any living cell is known to trigger a universal defense response, called heat-shock response, with rapid induction of tens of different heat-shock proteins. Bacterial heat-shock genes are transcribed by the σ32-bound RNA polymerase instead of the normal σ70-bound RNA polymerase. In this study, the diversity in sequence, variation in secondary structure and function amongst the different functional regions of the proteobacterial σ32 family of proteins, and their phylogenetic relationships have been analyzed. Bacterial σ32 proteins can be subdivided into different functional regions which are referred to as regions 2, 3, and 4. There is a great deal of sequence conservation among the functional regions of proteobacterial σ32 family of proteins though some mutations are also present in these regions. Region 2 is the most conserved one, while region 4 has comparatively more variable sequences. In the present work, we tried to explore the effects of mutations in these regions. Our study suggests that the sequence diversities due to natural mutations in the different regions of proteobacterial σ32 family lead to different functions. So far, this study is the first bioinformatic approach towards the understanding of the mechanistic details of σ32 family of proteins using the protein sequence information only. This study therefore may help in elucidating the hitherto unknown molecular mechanism of the functionalities of σ32family of proteins.