Ribosomes, preparation from cultured cells

These types of density labeling procedures provide a means of isolating replicating DNA sequences at any time during the S phase. There are other methods of analyzing the time of replication of specific classes of DNA sequences. For example, the time of replication of ribosomal RNA cistrons in synchronously growing hamster cells has been followed (Amaldi et al., 1969). Here DNA preparations were obtained from cultures at... 

The results presented in Fig. 17 show that mitochondria prepared in the presence of Mg from a log-phase culture of cells had a buoyant density in sucrose of 1.249 g/ml (Fig. 17A). However, if these mitochondria were washed with buffer containing 2 mM EDTA, a condition which will remove ribosomes from membranes, the mitochondrial density decreased markedly to 1.208 g/ml (Fig. 17C). When a log-phase culture of cells was starved for 1 h at 30°C, the mitochondria isolated in the presence of Mg were less dense (Fig. 17B) than mitochondria isolated from log-phase cells (Fig. 17A). In addition, mitochondria prepared from stationary-phase cells had a buoyant density of about 1.21 g/ml, considerably less than that of mitochondria prepared from log-phase cells. 

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