A system for the screening of reversions in an arginine-dependent strain of Neurospora has been developed.Reversion resulted from any one of three events:(a) Back mutation of the original arg gene.(b) Forward mutation at the pyr locus. This has the pleiotropic effect of suppressing arg while determining a pyrimidine requirement. Interaction with the unmutated nuclei of the same conidium permits growth on minimal medium.(c) Forward mutation at the pyr locus to alleles of intermediate activity. These alleles suppress arg, but do not create a pyrimidine requirement.
The divalent cation ionophore A23187 was found to induce apical branching in Neurospora crassa. Optimal effects were obtained by treatment with 0.1 mM ionophore for 30 min. Branching first became manifest during or shortly after treatment; successive rounds of branching could be observed at later times. Calcium starvation of the mycelium markedly reduced its subsequent response to the ionophore, whereas starvation for other divalent cations had no detectable effect. The branching response was markedly reduced in the presence of 10 to 30 mM cyclic AMP or derivatives thereof.
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