Characterization and sequence comparison of temperature-regulated chaperonins from the hyperthermophilic archaeon Archaeoglobus fulgidus

We have cloned and sequenced the genes encoding two chaperonin subunits (Cpn-α and Cpn-β), from Archaeoglobus fulgidus, a sulfate-reducing hyperthermophilic archaeon. The genes encode proteins of 545 amino acids with calculated M_r of 58 977 and 59 683. Both proteins have been identified in cytoplasmic fractions of A. fulgidus by Western analysis using antibodies raised against one of the subunits expressed in Escherichia coli, and by N-terminal amino acid sequencing of chaperonin complexes purified by immunoprecipitation. The chaperonin genes appear to be under heat shock regulation, as both proteins accumulate following temperature shift-up of growing A. fulgidus cells, implying a role of the chaperonin in thermoadaptation. Canonical Box A and Box B archaeal promoter sequences, as well as additional conserved putative signal sequences, are located upstream of the start codons. A phylogenetic analysis using all the available archaeal chaperonin sequences, suggests that the α and β subunits are the results of late gene duplications that took place well after the establishment of the main archaeal evolutionary lines.