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

Abstract

Studies on heterokaryons forced between sorbose-resistant (transport-defective) mutants of Neurospora crassa and a sorbose sensitive (transport-intact) wildtype strain showed that the mutants sorr A-l and sorr B-57 mapping in separate linkage groups, are recessive to wildtype; a 3rd mutant, not linked to the others, shows intermediate expression of the resistance character for one of 2 criteria considered. The functional relations between sorr-loci A and B and the amount of resistance caused by defects in both of them were investigated in forced heterokaryons of the type A"B + A"B, AB"+ AB." and AB + 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.