Genetic determinant in Escherichia coli affecting thymineless death and ultraviolet sensitivity.

We have infected Escherichia coli strain B3 with F' factors carrying different lengths of the K-12 chromosome. When the F' factor carries the tsx to purE segment, the resulting hybrid merodiploid shows increased sensitivity to thymineless death, although leaky deoxyribonucleic acid synthesis is unaffected, as well as increased sensitivity to ultraviolet irradiation. The dominant or partially dominant character of the effect indicates that it is not a product of allelic differences between E. coli K and B at either ras or lon.