Fig. 5. Bst impairs ribosome biogenesis. (A) Bst/+ causes a decrease in processed rRNAs. C57BLKS Bst/+ and +/+ littermates were fasted for 48 hours and re-fed for 2 hours. Tissue RNAs were radiolabeled by an intraperitoneal ³²P injection at the start of the re-feeding period. (left) Autoradiogram of pulse-labeled liver RNA (5 µg/lane). Mature 18S and 28S rRNAs and 34S and 45S precursors are indicated. (center) Methylene Blue stain of the same filter, showing total RNA. (right) Density tracing of autoradiogram showing that Bst has a greater effect on 28S rRNA. The Bst/+ profile is scaled twofold to equalize 18S rRNA levels. The relative peak areas measured for 45S, 34S, 28S and 18S rRNAs are 0.9, 1.1, 5.9 and 4.2 (+/+) and 0.9, 1.1, 1.5 and 1.8 (Bst/+), respectively. (B) Sucrose gradients of liver homogenates from normally fed +/+ and Bst/+ adult littermates. UV absorbance peaks corresponding to ribosomal subunits and polysomes are labeled. A prominent shoulder is present between the 60S and 80S subunits (arrowhead).