Cloning,expression and evolution of the gene encoding the elongation factor 1A from low thermophilic Sulfolobus solfataricus strain

The gene encoding the elongation factor 1K (EF-1K) from the archaeon Sulfolobus solfataricus strain MT3 (optimum growth temperature 75‡C) was cloned, sequenced and expressed in Escherichia coli. The structural and biochemical properties of the purified enzyme were compared to those of EF-1K isolated from S. solfataricus strain MT4 (optimum growth temperature 87‡C). Only one amino acid change (Val15CIle) was found. Interestingly, the difference was in the first guanine nucleotide binding consensus sequence G13HIDHGK and was responsible for a reduced efficiency in protein synthesis, which was accompanied by an increased affinity for both guanosine diphosphate (GDP) and guanosine triphosphate (GTP), and an increased efficiency in the intrinsic GTPase activity. Despite the different thermophilicities of the two microorganisms, only very marginal effects on the thermal properties of the enzyme were observed. Molecular evolution among EF-1K genes from Sulfolobus species showed that the average rate of nucleotide substitution per site per year (0.0312U1039) is lower than that reported for other functional genes.