Effect of 5-fluorouracil and cycloheximide on the early development of Phycomyces blakesleeanus spores and the activity of N-acetylglucosamine synthesizing enzymes.

The development of germinating Phycomyces spores was not inhibited by 5-fluorouracil (1mM) until the emergence of the germination tube. Fluorouracil was incorporated into RNA as efficiently as uracil; it did not inhibit the synthesis of proteins and the increase in respiratory activity during early development. Cycloheximide inhibited development as well as the increase in respiration and protein synthesis. This suggested that protein synthesis or some other cycloheximide dependent process, but no mRNA synthesis, was needed for the first developmental stages. The activity of two enzymes involved in the synthesis of N-acetylglucosamine increased markedly during germination. THis increase was inhibited by both 5-fluorouracil and cycloheximide; this suggested that those enzymes were synthesized on mRNA formed during germination.