Action of Mycophenolic Acid on Unstable Diploids of Penicillium chrysogenum

Abstract

DIPLOIDS of Penicillium chrysogenum heterozygous for the genes y/Y (yellow versus green conidia) and w/W (white versus green conidia) have green conidia. On plating, these give rise to a majority of green colonies, together with a small percentage (less than 1 per cent) of yellow or white colonies, or green colonies with white and/or yellow sectors. The proportion of these ‘segregant’ colonies and sectors is strongly increased (by more than 20–30 per cent) if the conidia are treated with the nitrogen mustard, methyl-bis(β-chloroethyl)amine (HN–2) or with X-rays¹. When certain of the colonies with sectors are sub-cultured by the plating of green conidia, they give rise to a population of colonies with sectors ; these colonies maintain the unstable character indefinitely in successive transfers. A dozen unstable clones were isolated, each of which showed sectors with a single phenotype (rarely two) characterized by the presence of nutritional markers as well as by the colour of the conidia. Manganous chloride, added to the agar medium at 40 mM concentration, inhibited the production of sectors with nearly all the unstable clones; the inhibition, however, was not of a permanent nature, and disappeared when the clones were subcultured on medium free from manganous chloride².