The assignment of four new loci, including the coumarin sensitivity locus couA, to linkage group VII of Dictyostelium discoideum.

The assignment to linkage group VII of the coumarin sensitivity mutation couA351, which leads to a loss of colony-forming ability on agar containing coumarin, was established using the linkage group VII markers cobA1 and tsgK21. Complementation of the couA351 and bsgA5 mutations was an effective method of selecting heterozygous diploids at 21 +/- 1 degree C, i.e. without requiring a temperature sensitivity mutation. A morphological mutation, frtB353, which affects the distribution of fruiting bodies was also assigned to linkage group VII. Both the couA351 and frtB353 mutations were discovered in the tsgK21 strain NP187. Eight independently isolated, recessive mutations leading to resistance of 300 micrograms CoCl2 ml-1 were allelic with the cobA1 mutation. The partially dominant cob-353 mutation was shown to map in linkage group VII on the basis of its segregation relative to the couA351 and tsgK21 mutations and is almost certainly an allele of the cobA locus. These results are consistent with there being only a single locus at which mutations can lead to resistance to high concentrations of CoCl2. Two temperature sensitivity mutations tsgM357 and tsgG4 were also assigned to linkage group VII.