Abstract
The orientation of 3 transducing fragments of Salmonella typhimurium which contain known operons was determined on the chromosome by F-factor-mediated conjugation. The tryptophan and histidine operons are polarized clockwise, for the structural genes are located clockwise from the operator gene, while the leucine operon is polarized counterclockwise. This indicates that the direction of information transfer is reversed in different operons.