Levels of RNA polymerase activities during growth, encystment and germination ofPhysarum polycephalum

Two RNA polymerases, enzyme A and enzyme B, were prepared fromPhysarum plasmodia. They are not located in the cytosol. Isolated nuclei, however, contain only a fraction of the total RNA polymerase activity: 1.5-19% depending on the nuclear preparation method.The level of RNA polymerase B shows little variation at developmental stages of growth and encystment, or in cysts and during germination, whereas RNA polymerase A displays a marked transient decrease in activity during the stationary growth phase before encystment.