Differences in RNA formation and polyribosome metabolism in serum-starved normal and transformed cells.

Comparative studies of RNA synthesis and polyribosome metabolism in normal (RFL) and transformed (RFL-T) cells under serum starvation show that their growth is more or less dependent upon serum factor. By limiting serum in the medium, 80 to 90% of RNA or protein synthesis is inhibited in RFL cells, while in RFL-T cells macromolecular synthesis proceeds at one-third to one-fourth the rate of control. Ribosomal RNA synthesis is more preferentially blocked in untransformed cells under decreased protein synthesis caused by serum deprivation than in transformed cells. However, when both RFL and RLF-T cell lines are treated with cycloheximide, 2 /xg/ml, which inhibits over 90% protein synthesis, little if any ribosomal RNA is produced. Also, analysis of cytoplasmic extracts with isokinetic sucrose density gradient centrifugation shows the greater transition of polyribosomes into monosomes in RFL-T cells compared to that of RFL cells with time of serum deprivation. The prominent redistribution of polyri bosomes, which occurred in serum-starved RFL-T cells but not in RFL cells, is restored by addition of 0.2 /ig/ml to 2.0 /ig/ml cycloheximide. Since nascent peptides are be ing made in polyribosomes of RFL-T starved for serum but little if any peptide chains are made in RFL, the ribo somal transition requires peptide formation at a reduced level.