The peptidyl-puromycin reaction with Neurospora crassa ribosomes

The reaction of the peptidyl-tRNA in an “in vitro” system from Neurospora crassa with puromycin has been studied by different experimental approaches. Ribosomes precharged with labelled polyphenylalanine have been prepared and the release of radioactivity, occurring after the reaction with puromycin, has been followed on sucrose density gradients. Furthermore the reaction of endogenous peptidyl-tRNA carried by ribosomes isolated from actively growing mycelia with 3H-puromycin has been characterized. By this latter technique it has been possible to evaluate the percentage of ribosomes engaged in protein synthesis in ribosomal populations isolated from mycelia in different stages of growth.