CONSEQUENCES OF DELETION MUTATIONS JOINING 2 OPERONS OF OPPOSITE POLARITY

We have studied the levels of the enzymes corresponding to the genes remaining in deletion mutations linking the histidine and rough B operons of Salmonella typhimurium. Such deletion mutations leave the two promoter regions intact, as the two operons are oriented in opposite directions. Derepression of the histidine operon leads to a fivefold decrease in the rate of synthesis of the enzyme corresponding to the first intact rfb gene adjacent to the end of the deletion. When the histidine operon is repressed, there is no inhibition of any rough B enzyme, but the rate of synthesis of the enzyme corresponding to the first intact his gene adjacent to the end of the deletion is decreased fourfold. Studies of the rate of synthesis of the his enzyme corresponding to the gene adjacent to the end of a deletion, at several levels of partial derepression, are consistent with a simple model of interference between the RNA transcription apparatus of the two operons. © 1969.