Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpinloop structure

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. The heat shock response is a widespread phenomenon that involves the induction of the synthesis of a large number of proteins following stress situations, such as a shift to higher temperatures. Several of these proteins are highly con-served, especially proteins encoded by dnaK (Hsp7O) and groEL (Hsp6O) (for reviews, see references 16, 17, and 25)