Structures of chaperonins from an intracellular symbiont and their functional expression in Escherichia coli groE mutants

The gene coding for the synthesis of symbionin in the aphid endosymbiont was sequenced and assessed for chaperonin functions. Sequence data from a 2,739 bp fragment indicated that the symbionin-coding region was bicistronic, and therefore designated as sym operon. The operon consisted of symL and symS genes, which by complementation analysis with gro-mutants of Escherichia coli, was shown to be analogous to E. coli chaperonins. Amino acid sequence comparisons confirmed this finding. The results suggest that symbionin is a molecular chaperone, and is involved in the assembly of polypeptides imported into the endosymbiont from the host cell.