"No-growth"-Complementation in Forced Heterokaryons from Sorbose-Resistant (Transport-Defective) Neurospora crassa Mutants

Studies on heterokaryons forced between sorbose-resistant (transport-defective) mutans of Neurospora crassa and a sorbose-sensitive (transport-intact) wildtype strain show that mutants sorr A-l and sorr B-57, mapping in separate linkage groups, are recessive to wildtype; a third mutant, not linked to the others, shows intermediate expression of the resistance character for one of two criteria considered. The functional relations between sorr-loci A and B and the amount of resistance caused by defects in both of them have been investigated in forced heterokaryons of the type A~B-\-A~B, AB~ + AB~ and A~B + AB~. Pairwise combination of A~ with B~ resulted in complementation to the sorbose-sensitive wild-phenotype ("no-growth" complementation). The occurrence of no-growth complementation in the double heterozygote supports the conclusion derived earlier that both gene loci A and B are coding for permeases responsible for the uptake of sorbose.