Changes in ribosomal RNA processing paths in resting and phytohemagglutinin stimulated guinea pig lymphocytes

Processing of rRNA was examined in resting and phytohemagglutinin stimulated guinea pig lymphocytes. Synthesis of 1.7 (28S) and 0.7 (18S) X 10⁶ dalton rRNA was more than 4 fold greater in phytohemagglutinin stimulated than in resting cells. A 5 to 10 fold increase in flux of molecules through a 2.3 x 10⁶ dalton RNA occurred without a concurrent change in the flux through a 2.6 x 10⁶ dalton fraction in phytohemagglutinin stimulated cells. In both resting and phytohemagglutinin stimulated lymphocytes, the 2.3 x 10⁶ dalton intermediate equilibrated with [³H]methyl label and pulse chased prior to the 2.6 x 10⁶ dalton RNA. The data indicate at least two processing paths in guinea pig lymphocytes; one proceeds to rRNA via a 2.3 x 10⁶ dalton intermediate, and another proceeds via a 2.6 x 10⁶ dalton RNA. The increase in rRNA synthesis in phytohemagglutinin stimulated cells occurs primarily through that path containing the 2.3 x 10⁶ dalton intermediate.