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The structural gene (pgk) encoding 3-phosphoglycerate (PGK) from Bacillus
stearothermophilus NCA1503, has been cloned in Escherichia coli and its complete
nucleotide sequence determined. The gene consists of an open reading frame
corresponding to a protein of 394 amino acids (aa) (calculated Mr 42,703) and,
in common with other prokaryotic pgk genes, is preceded by the structural gene
encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Constructs containing
the B. stearothermophilus pgk gene and its flanking sequences in the high-copy
plasmid, pUC9, co-express both PGK and GAPDH at high levels in transformed E.
coli cells, typically producing PGK at levels of up to 30% of the soluble cell
protein. The deduced aa sequence of B. stearothermophilus PGK is compared with
those of the mesophilic (yeast) and extreme thermophilic (Thermus thermophilus)
enzymes since the crystal structure of these PGKs are known or are in the
process of being determined. Changes in the sequences of the three enzymes, as
they appear to relate to the enhancement of thermal stability, are discussed.
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