Genetic complementation in Cryptococcus neoformans.

A complementation test was devised for the fungus Cryptococcus neoformans. Complementation was signalled by the growth of prototrophic heterokaryons generated in crosses of the type aB X Ab, where a and b represent any two of the genetic markers ilv1, cys1, cys2, and cys3. The cloned complementing heterokaryons formed characteristic hyphal colonies that contained both hyphae and yeast cells. The heterokaryon-derived yeasts were of three kinds: parental haploids, recombinant haploids, and diploids.