Molecular cloning and sequencing of the β-isopropylmalate dehydrogenase gene from the cyanobacterium Spirulina platensis

Summary: The gene for β-isopropylmalate dehydrogenase (EC 1.1.1.85) of Spirulina platensis (leuB) was cloned from a γEMBL3 genomic library by heterologous hybridization using the Nostoc UCD 7801 leuB gene as a probe. The sequence of the entire leuB coding region was determined as well as 645 bp of 5’ flanking region and 956 bp of 3’ flanking region. DNA sequencing revealed an open reading frame of 1065 nucleotides capable of encoding a polypeptide of 355 amino acids. Homologies between the amino acid sequence deduced from the nucleotide sequence of the S. platensis leuB gene and the amino acid sequences published for corresponding proteins either from bacteria or yeasts are 45% or more. Northern hybridization analysis indicated that the S. platensis leuB gene is transcribed as a single monocistronic RNA of approximately 1200 bases.