Chromosome rearrangements in isolates that escape from<Emphasis Type="Italic"> het-c</Emphasis> heterokaryon incompatibility in<Emphasis Type="Italic"> Neurospora crassa</Emphasis>

Chromosomal rearrangement is implicated in human cancers and hereditary diseases. Mechanisms generating chromosomal rearrangements may be shared by a variety of organisms. Spontaneous chromosomal rearrangements, especially large deletions, take place at high frequency in isolates that escape from heterokaryon incompatibility in Neurospora crassa. In this study, chromosomal rearrangements were detected in strains that had escaped from het-c heterokaryon incompatibility in N. crassa. A vc1 mutant carried a 20-kbp deletion covering five ORFs. A vc2 mutant carried a complex chromosome rearrangement with an 8-kbp deletion covering three ORFs, a 34-bp deletion and an 80-kbp inversion. The break-points of chromosome rearrangements in the vc1 and vc2 mutants all have direct repeats of 2 bp, similar to the break-points of some chromosome rearrangements associated with human cancer and genetic diseases. An ahc mutant carried a 31-kbp deletion covering at least 11 ORFs and a het-c deletion mutant carried a 7-kbp deletion covering two ORFs. Additional chromosomal rearrangements occurred in these two strains. These results indicate that escape from heterokaryon incompatibility can be used as a model system for chromosome rearrangement and DNA-repair studies. The impact of the chromosomal rearrangements is discussed, especially the deletion of the predicted ORFs on the phenotype of mutants.Communicated by U. Kück