EFFECTS OF LIQUID HOLDING ON INDUCTION OF MUTATIONS IN AN ULTRAVIOLET-SENSITIVE STRAIN OF ASPERGILLUS NIDULANS

It has been shown that a mutation to UV-sensitivity (uvs-I) has the effect of reducing the yield of adenine-independent mutants in Aspergillus nidulans whether the comparison is made on the basis of dose or survival. Methionine-independent mutants were induced with a greater frequency only at higher doses of UV and lower levels of survival. When the uvs-I strain is held at 25° in buffer following UV treatment, survival increases to a maximum at between 48 and 96 h. The level of survival attained by the UV-sensitive mutant during liquid holding is equivalent to that observed with a uvs+ strain plated immediately following UV treatment or after 96 h of liquid holding. The uvs-I mutation allows for the expression of liquid-holding repair of UV damage in A. nidulans. The yield of both adenine- or methionine-independent mutants based on survival increased during liquid holding of the uvs-I strain to a level greater than that observed in an equivalent uvs+ strain. The yield of adenine- or methionine-independent mutants in the uvs+ strain was not altered significantly during liquid holding. We interpret the uvs-I mutant of A. nidulans to represent a regulatory mutation in a function concerned with the repair of radiation damage which in addition to affecting the rate of repair leads to reduced fidelity of repair. © 1969.