The organization and expression of the pyruvate dehydrogenase complex genes, (E1), (E2) and (E3), were investigated using a series of λ transducing phages carrying different segments of the region of the chromosome of The polypeptides synthesized following the infection of u.v.-irradiated lysogenic and non-lysogenic hosts were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography.

The and gene products were readily identified by their sizes, 100000 (pyruvate dehydrogenase. E1 component) and 56500 (lipoamide dehydrogenase. E3 component), but considerable heterogeneity was detected for the gene product (acetyltransferase, E2 component). The main E2 polypeptides, 80000 and 83000, were accompanied by a family of minor polypeptides. 86000, 89000 and 91000, but no precursor-product relationships were apparent. A very large polypeptide, 190000, was also detected and found to contain the E1 component but in uncertain combination. In addition, the product of a gene in the region was detected as a polypeptide with 36500.

The existence of a single promoter for the and genes and a separate promoter for the gene was confirmed. The gene was shown to be transcribed with the same polarity as the genes (clockwise with respect to the linkage map). The relative rates of expression of the three genes from the bacterial promoters were estimated as 0.94:1.0:1.4-2.3 (E1:E2:E3) on a molar basis. The excess production of lipoamide dehydrogenase components (E3) indicates that the promoter functions independently, at least in supplying components for the 2-oxoglutarate dehydrogenase complex. When expressed from P, the powerful phage promoter, the and lpd gene products accounted for the greater part of the newly synthesized protein.


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