Chromosome rearrangements in Dictyostelium discoideum

A tandem duplication (D350(III,III] of the whiB to radB interval of linkage group III has been characterized. The gene order on the duplication-bearing chromosome is: centromere, whiB500, radB+, whiB+, radB24, bsgA5, acrC4. Slow-growing, duplication-bearing strains (yellow-spored, radiation-resistant) produced four classes of faster growing sectors involving the whiB and radB loci: white-spored, radiation-sensitive (whiB500, radB24); white-spored, radiation-resistant (whiB500, radB+); yellow-spored, radiation-sensitive (whiB+, radB24); and yellow-spored, radiation-resistant. The first three classes can be explained as the products of single recombination events in which one copy of the whiB to radB interval was lost. The yellow-spored, radiation-resistant sectors probably arose by mutation elsewhere in the genome, but alternatively may represent multiple recombination events or deletion of part of one copy of the duplicated region. Loss of the duplicated segment was enhanced by irradiation with ultraviolet light (254 nm). Heterozygosity for a DNA repair mutation at the radB locus may have been involved in the formation of the duplication. It is proposed that translocations are a major cause of nonrandom segregation patterns such as the cosegregation of unlinked markers in Dictyostelium discoideum. Translocations involving all known linkage groups are tabulated and DNA damage by N-methyl-N'-nitro-N-nitrosoguanidine is implicated in the formation of translocations in D. discoideum.