Abstract
BackgroundBacterial GreA is an indispensable factor in the RNA polymerase elongation complex. It plays multiple roles in transcriptional elongation, and may be implicated in resistance to various stresses.Methodology/Principal FindingsIn this study, we show that Escherichia coli GreA inhibits aggregation of several substrate proteins under heat shock condition. GreA can also effectively promote the refolding of denatured proteins. These facts reveal that GreA has chaperone activity. Distinct from many molecular chaperones, GreA does not form stable complexes with unfolded substrates. GreA overexpression confers the host cells with enhanced resistance to heat shock and oxidative stress. Moreover, GreA expression in the greA/greB double mutant could suppress the temperature-sensitive phenotype, and dramatically alleviate the in vivo protein aggregation. The results suggest that bacterial GreA may act as chaperone in vivo.Conclusions/SignificanceThese results suggest that GreA, in addition to its function as a transcription factor, is involved in protection of cellular proteins against aggregation.
Highlights
RNA synthesis is a conserved biochemical reaction mediated by DNA-dependent RNA polymerase (RNAP) in all organisms
We show that the transcriptional elongation factor GreA suppresses
The activity of GreA is not so effective as DnaK, concerning the small molecular size and its main function as a transcription factor, we propose that the chaperone activity is notable
Summary
RNA synthesis is a conserved biochemical reaction mediated by DNA-dependent RNA polymerase (RNAP) in all organisms. GreA and its homolog, GreB, are involved in the transition from transcription initiation to elongation [5], as they may facilitate the escape of the RNAP complex from certain promoters Both proteins have been reported to act as transient catalytic components of RNA polymerase [6]. The ‘‘L-shaped’’ structure is shared by some proteins with molecular chaperone activity, such as FimC [9], PapD [10], HscB [11], and SfaE [12] In these proteins, 2 immunoglobulin-like domains are located at an approximate 90u to each other with a large cleft between them. A greA and greB double-mutant strain is not able to survive at high temperatures [17] Together, these data indicate that GreA may play important roles in stress resistance, in addition to its role in transcription elongation. We propose that in addition to its function as a transcription factor, GreA may play a role in protein quality control in vivo
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