MOLECULAR CHARACTERIZATION OF AN ESCHERICHIA-COLI MUTANT WITH A TEMPERATURE-SENSITIVE MALONYL COENZYME A-ACYL CARRIER PROTEIN TRANSACYLASE

The temperature-sensitive malonyl CoA-ACP transacylase found in the Es cherichia coli strain LA2-89, carrying the fabD89 allele, was shown to result from the presence of an amber mutation in the fabD gene, at co don position 257, in combination with the supE44 genotype of this stra in. The truncated form of the protein produced as the result of the am ber mutation was demonstrated to be enzymatically inactive, whereas am ber suppression rendered the resulting enzyme temperature labile. Site -directed mutagenesis of codon 257 revealed a requirement for an aroma tic amino acid at this position in the polypeptide chain, to assure te mperature stability of the enzyme.