Nuclear Segregation and the Growth of Clones of Bacterial Mutants induced by Ultraviolet Light

Abstract

SUMMARY: Histidine-independent (h+) mutants induced in histidine-requiring (h-) cultures by ultraviolet light have a delay in the onset of logarithmic increase that is about two generations longer than the delay shown by marked unirradiated h+ bacteria present at the same time. This extra delay is interpreted as being due to the segregation of one from four nuclei which are present, on the average, in growing h- organisms. The same assumption accounts for the extra delay observed in spontaneous h+ mutants. These and other results are discussed in relation to the site of mutation and to the various types of delay that can retard the onset of growth of a mutant clone. It is concluded that in the mutation from h- to h+, the h+ condition is dominant in the heterocaryon, that whatever phenotypic delay exists is short, and that cell division is not required to pass through it.