Carboxylase genes of Sulfolobus metallicus

Carbon dioxide limitation of Sulfolobus metallicus resulted in increased ce llular concentrations of polypeptides that were predicted to be biotin carb oxylase and biotin carboxyl-carrier-protein components of a protein complex . These polypeptides were coeluted from a native polyacrylamide gel and wer e estimated at 19 and 59 kDa after separation by denaturing gel electrophor esis. Their encoding genes were identified, sequenced and shown to code for polypeptides of 18,580 and 58,235 Da with similarities to biotin carboxyl carrier proteins and biotin carboxylases, respectively. The genes overlappe d at the second of two stop codons that terminated the carboxylase gene. A third gene occurred on the opposite strand, 293 bp upstream of the biotin c arboxylase gene. Its deduced amino acid sequence was similar to those of ca rboxyl transferase subunits of carboxylase enzymes, in particular to those of the propionyl-CoA carboxylases. It is proposed that the three described genes could encode the key enzyme complex responsible for carbon dioxide fi xation during autotrophic growth of the thermoacidophilic archaea.