The gene tkt for the enzyme transketolase (TK; EC 2.2.1.1) of Escheric
hia coli K-12 was subcloned and the complete DNA sequence was determin
ed from both strands. An open reading frame with 1992 bp was detected
that could encode a protein with a subunit mass of 72 143. The gene fo
rms a monocistronic operon and is transcribed counterclockwise to the
E. coli chromosome. From recombinant strains, the enzyme was purified
and 39 N-terminal amino acid residues were determined. The DNA-derived
protein sequence showed 49.5% identical amino acid residues with the
transketolase of Rhodobacter sphaeroides, 46.8% identity with the enzy
me from Saccharomyces cerevisiae, and 28.9% identity with the human tr
ansketolase.