HEAT-SHOCK TRANSCRIPTION OF THE GROESL OPERON OF AGROBACTERIUM-TUMEFACIENS MAY INVOLVE A HAIRPIN-LOOP STRUCTURE

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