Molecular cloning and expression of Spirulina platensis acetohydroxy acid synthase genes in Escherichia coli

The coding sequence for Spirulina platensis acetohydroxy acid synthase (AHAS, EC 4.1.3.18) is shown to be contained within a 4.2 Kb ClaI fragment (ilvX) that has been cloned from a recombinant lambda library. This fragment was able to complement a suitable mutant of Escherichia coli when inserted into the ClaI site of plasmid pAT153 in either orientation, demonstrating that transcription of ilvX originated within the cloned fragment. The probe used for hybridization experiments was the corresponding gene from Anabaena sp. PCC7120. The same probe allowed us to identify a second putative gene encoding AHAS in the S. platensis genomic library.