A mutation which modifies the activity of a translational suppressor in Aspergillus nidulans

A third type of translational fidelity mutation has been induced in Aspergillus nidulans. The new mutation enhances growth, in suppressing conditions, of a strain containing suppressor suaC109 and antisuppressor asuD14 and is called aloB8 for its allosuppressor activity. Compared with the progenitor strain (asuD14, suaC109), ribosomes from the new mutant (aloB8, asuD14, suaC109) increase misincorporation of leucine in a poly(U)-dependent homologous cell-free assay. The misreading level is maintained by ribosomes after washing with 500 mM KCl and suggests an alteration in a ribosomal component or a tightly bound factor. Ribosomes from an aloB8, asu+, sua+ strain also misread to a higher level than those of the control strain despite the fact that, in vivo, this mutation alone has no known suppressor activity. Mg2+ ions have been used in vivo for the first time to classify translation mutants.