Location of the Transketolase (tkt) Gene on the Escherichia coli Physical Map

Transketolase (EC 2.2.1.1) catalyzes the interconversion of sugar phosphates in the pentose phosphate cycle. Esche-nichia coli K-12 mutants with a defect in transketolase (tkt mutants) have been isolated (5), and a map position of 62 min was assigned. However, as P1-mediated cotransduction at-tempts with the markers argA, lysA, and serA had failed, this location remained unverified (2, 5). Recently, the tkt gene was cloned as a BamHI DNA fragment of about 6 kb from E. coli, but no chromosomal location was given (4). Independently, the gene was cloned on an RP4miniMu prime vector (8). Subcloning from this vector allowed us to locate the tkt gene on a 2.5-kb DNA (Sau3A partial plus KpnI) fragment present in plasmid pGSJ425 (9). The sequence of the insert DNA was deter-mined, and an open reading frame (ORF) of 1,992 bp was found. This could encode a protein subunit with a molecula