Alanyl-tRNA synthetase gene of the extreme acidophilic chernolithoautotrophic Thiobacillus ferrooxidans is highly homologous to alaS genes from all living kingdoms but cannot be transcribed from its promoter in Escherichia coli

1 Laboratoire de Chimie Bactérienne, Institut de Biologie Structurale et de Microbiologie, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France *Author for correspondence: Violaine Bonnefoy. Tel: + 33 4 91 16 41 46. Fax: + 33 4 91 71 89 14. e-mail: bonnefoy@ibsm.cnrs-mrs.fr ABSTRACT Summary: The alaS gene of Thiobacillus ferrooxidans has been cloned and sequenced and its expression in Escherichia coli and T. ferrooxidans analysed. The same genomic organization to that in E. coli ( recA-recX-alaS ) has been found in T. ferrooxidans. The recA and alaS genes cannot be transcribed 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 genes from bacteria, archaea and eucarya. Two regions, one of which corresponds to the catalytic core, are particularly well-conserved at the nucleotide sequence level, a possible indication of strong constraints during evolution on these parts of the genes. Keywords: Thiobacillus ferrooxidans, alanyl-tRNA synthetase, RecX