Growth-rate-dependent adjustment of ribosome function in chemostat-grown cells of the fungus Mucor racemosus

The dimorphic fungus Mucor racemosus was grown as a yeast in a chemostat. Cellular growth rates were varied over a fourfold range under an atmosphere of N2 and over an eightfold range under CO2. Under either atmosphere, an increase in the cellular growth rate resulted in increases in (i) the cellular ribosome concentration, (ii) the percentage of ribosomes active in protein synthesis, and (iii) the rate of polypeptide chain elongation. The rate of protein synthesis in this organism can therefore be regulated by adjustment of all of these mechanisms.