Interrupted mating methods were used to map the positions on the chromosome of genes for the utilization of acetamide, histidine and proline. An entry time of 22 min was found for a put marker determining the utilization of proline. Two groups of hut mutants were studied. Mutation hut-109 was located at 18 min and mutation hutU108, which results in a defect in urocanase activity, mapped at 28 min. hutU was shown by transduction with bacteriophage F116 to be linked to ser-3 but not to met-28 and ilv-202, giving a map order of hutU-ser-3-ilv-202-met-28.
The amidase genes were assigned an entry time of 65–75 min. A method is described for examining late entry markers by interrupted mating.