A temporal analysis of the synthesis of the mRNA sequestered in zoospores of Blastocladiella emersonii

To determine when the dormant mRNA of Blastocladiella emersonii zoospores is synthesized, the metabolism of poly(A) RNA and rRNA was studied during growth and sporulation using pulse-chase techniques. Zoospore poly(A) RNA is synthesized at all stages of the growth cycle investigated in cultures grown either on a normal 15-hr growth cycle or in minicyclic cultures induced to sporulate after only 6.5 hr growth. For cells labeled during the growth phase the specific activity of the pulse-labeled poly(A) RNA and rRNA was identical at the beginning and end of sporulation for any of the 2-hr labeling times investigated. From this it was concluded there is neither a preferential conservation nor degradation during sporulation of the poly(A) RNA and rRNA synthesized at various times during growth. Poly(A) RNA synthesized during early sporulation is preferentially degraded; in contrast, poly(A) RNA synthesized during late sporulation is conserved in the zoospore. Approximately one-third of the total zoospore poly(A) RNA accumulates during the final 15–20 min of sporulation. The accumulation rate for both poly(A) RNA and rRNA decreases as sporulation proceeds. In addition, the rate of degradation for both types of RNA decreases at later stages of sporulation.