Induction of inter- and intragenic mitotic recombination by fluorodeoxyuridine and fluorouracil in Aspergillus nidulans.

is known from the work of ESPOSITO and HOLLIDAY (1964) that fluorodeoxy‘:ridhe (FUDR) is a powerful inducer of mitotic crossing over in Ustilago. Recombination was also induced by GALLANT and SPOTTSWOOD (1965), causing thymidilate starvation through the action of FUDR. HOLLIDAY (1964a) has proposed that agents that increase recombination should be called ‘Lrecombinagens.” The purpose of the present paper is not only to relate the findings of HOLLIDAY to Aspergillus nidulans and to see if fluorouracil (FU) produces an analogous action, but also to determine whether the so-called recombinagens exert their action at both interand intragenic levels. We do not intend to investigate the way in which FUDR and FU act, but simply to see what genetical information can be obtained by the use of agents which increase recombination frequency. There is considerable evidence that in most fungi recombination at the intragenic level may operate by a mechanism distinct from that of intergenic crossing over (for general reviews see WESTERGAARD 1964 and HOLLIDAY 1964). The study of induction of recombination by means of recombinagens may throw some light on the nature of the mechanisms working at both levels.