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Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpin-loop structure.

ABSTRACT: The groESL operon of Agrobacterium tumefaciens was cloned and sequenced and found to be highly homologous to previously analyzed groE operons in nucleotides of the coding region and in amino acid sequence. Transcription of this operon in A. tumefaciens was considerably stimulated by heat shock. Primer extension analysis revealed that the groE transcripts from cells under heat shock were initiated from the same promoter (a sigma-70-like promoter) as transcripts from untreated cells, and no sequence homology with the Escherichia coli heat shock promoters was observed. The DNA sequence downstream of the transcription start site contains an inverted repeat that has a strong similarity to other groESL operons of both gram-positive and gram-negative bacteria (such as cyanobacteria and chlamydiae). This conserved region is thought to form a hairpin-loop structure and may play a role in gene regulation during heat shock.

SUBMITTER: Segal G

PROVIDER: S-EPMC204629 | biostudies-other | 1993 May

REPOSITORIES: biostudies-other

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Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpin-loop structure.

Segal G G Ron E Z EZ

Journal of bacteriology 19930501 10

The groESL operon of Agrobacterium tumefaciens was cloned and sequenced and found to be highly homologous to previously analyzed groE operons in nucleotides of the coding region and in amino acid sequence. Transcription of this operon in A. tumefaciens was considerably stimulated by heat shock. Primer extension analysis revealed that the groE transcripts from cells under heat shock were initiated from the same promoter (a sigma-70-like promoter) as transcripts from untreated cells, and no sequen ...[more]

PMID: 8098329

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Project description:Alpha-crystallin-type small heat shock proteins (sHsps) are ubiquitously distributed in most eukaryotes and prokaryotes. Four sHsp genes named hspL, hspC, hspAT1, and hspAT2 were identified in Agrobacterium tumefaciens, a plant pathogenic bacterium capable of unique interkingdom DNA transfer via type IV secretion system (T4SS). HspL is highly expressed in virulence-induced growth condition and functions as a VirB8 chaperone to promote T4SS-mediated DNA transfer. Here, we used genetic and biochemical approaches to investigate the involvement of the other three sHsps in T4SS and discovered the molecular basis underlying the dominant function of HspL in promoting T4SS function. While single deletion of hspL but no other sHsp gene reduced T4SS-mediated DNA transfer and tumorigenesis efficiency, additional deletion of other sHsp genes in the hspL deletion background caused synergistic effects in the virulence phenotypes. This is correlated with the high induction of hspL and only modest increase of hspC, hspAT1, and hspAT2 at their mRNA and protein abundance in virulence-induced growth condition. Interestingly, overexpression of any single sHsp gene alone in the quadruple mutant caused increased T4SS-mediated DNA transfer and tumorigenesis. Thermal aggregation protecting assays in vitro indicated that all four sHsps exhibit chaperone activity for the model substrate citrate synthase but only HspL functions as efficient chaperone for VirB8. The higher VirB8 chaperone activity of HspL was also demonstrated in vivo, in which lower amounts of HspL than other sHsps were sufficient in maintaining VirB8 homeostasis in A. tumefaciens. Domain swapping between HspL and HspAT2 indicated that N-terminal, central alpha-crystallin, and C-terminal domains of HspL all contribute to HspL function as an efficient VirB8 chaperone. Taken together, we suggest that the dominant role of HspL in promoting T4SS function is based on its higher expression in virulence-induced condition and its more efficient VirB8 chaperone activity as compared to other sHsps.

Dataset Information

Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpin-loop structure.

Publications

Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpin-loop structure.

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