Abstract
Amebae of Naegleria gruberi undergo phenotypic transformation into flagellates when the aqueous environment is changed from axenic growth medium to non-nutrient buffer. This differentiation, which requires 80 min at 25 °C, is dependent on transcription during the first 40 min. The nature of the RNA synthesized during differentiation is the subject of this report. Net synthesis of RNA continues for the first 30 min after differentiation is initiated, but thereafter degradation exceeds synthesis leading to an overall decrease of 6 % in total RNA per cell by 90 min. [14C]-Uracil is incorporated into RNA during differentiation. Incorporation is linear until roughly 10 min before the appearance of flagella, at which time the rate of incorporation declines. Sucrose gradient analysis has been used to compare the RNA synthesized by cells differentiating in buffer versus amebae in growth medium. There is proportionally more synthesis of messenger-like RNA and less of rRNA in differentiating cells. The messenger-like RNA synthesized during differentiation is heterogeneous in size, but very large molecules (> 45 S) have not been found. This rapidlylabeled RNA is first present in the nucleoplasm, and moves rapidly to the cytoplasm, reaching equilibrium within 10 min. In the cytoplasm it is found associated with polysomes, where it has the EDTA and ribonuclease sensitivity expected of mRNA. These observations support the interpretation that the rapidlylabeled RNA is mRNA. It is not yet known whether this mRNA includes the RNA essential for differentiation.