Published online by Cambridge University Press: 14 April 2009
The brlA12 variegated position effect mutant is particularly suited for tests of environmental and genetic influences on variegation, but out of a large number of substances added to the medium, only salts at high concentrations and methylamine significantly increased expression of this gene. Medium shifting experiments showed that brlA12 activity could be switched on late, but once active, was rarely switched off again during conidiation. Separate brlA12 clones in heterokaryons were activated independently. Some brlA12-specific suppressor mutants, including those at loci giving almost complete suppression, have been studied. One class of suppressors also confers inability to utilize galactose as carbon source and comparison with other, pre-existing mutants showed that the brlA12 phenotype was either suppressed or enhanced by mutants with complex phenotypes involving galactose utilization, molybdate resistance, acid phosphatase production and sulphur metabolism. Tests for the involvement of DNA methylation in brlA12 expression gave negative results.