Entamoeba histolytica: Autoradiographic analysis of nuclear sites of RNA synthesis

Abstract

Autoradiographs of sectioned Entamoeba histolytica labeled with [5- 3H]uridine for time periods ranging from 15 sec to 24 hr revealed (1) some evenly distributed nuclear label and (2) extensive labeling of the peripheral nuclear chromatin. This nuclear area is the probable site of synthesis (or accumulation) of ribosomal RNA and/or ribosomal precursor RNA. Also seen was (3) evenly dispersed cytoplasmic label with peaks of labeling after ca. 48 hr of exposure to isotope. Pulses of 5 min, 15 min, 1 hr, and 2 hr followed by a 5-min to 3-hr chase in unlabeled medium with carrier uridine demonstrated that most of the pulse-labeled nuclear RNA was lost from the nucleus; however, a small amount of stable nuclear RNA was detected after a 2- to 3-hr chase. Further, an instability of cytoplasmic RNA was also detected.