ALANYL-TRANSFER-RNA SYNTHETASE GENE OF THE EXTREME ACIDOPHILIC CHEMOLITHOAUTOTROPHIC THIOBACILLUS-FERROOXIDANS IS HIGHLY HOMOLOGOUS TO ALASGENES FROM ALL LIVING KINGDOMS BUT CANNOT BE TRANSCRIBED FROM ITS PROMOTER IN ESCHERICHIA-COLI

The alaS gene of Thiobacillus ferrooxidans has been cloned and sequenc ed and its expression in Escherichia coli and T. ferrooxidans analysed . The same genomic organization to that in E. coil (recA-recX-alaS) ha s been found in T. ferrooxidans. The recA and alaS genes cannot be tra nscribed from their own promoters in E. coli. In addition to the well- known homology at the protein level between AlaS proteins from various organisms, a strong homology was found between all the known alaS gen es from bacteria, archaea and eucarya. Two regions, one of which corre sponds to the catalytic core, are particularly well-conserved at the n ucleotide sequence level, a possible indication of strong constraints during evolution on these parts of the genes.