Autoradiography following hybridization with three probes complementary to 18S rRNA indicated the presence of five fragments (A-E) with approximate sizes of 1000, 800, 600, 500, and 300 nts (Fig. 4 A) . The putative 18S rRNA cleavage pattern suggested that fragments A (approximately 1000 nts) and B (approximately 800 nts) are derived from intact 18S rRNA, whereas the remaining fragments (C, D, and E, approximately 600, 500, and 300 nts, respectively) resulted from further secondary cleavage of the two primary fragments (C and E from A and D from B) (Fig. 4B) .