Rates of synthesis of ribosomal protein and total ribonucleic acid through the cell cycle of the fission yeast Schizosaccharomyces pombe

Abstract

The rates of synthesis of ribosomal proteins through the cell cycle of the fission yeast Schizosaccharomyces pombe have been examined by spec. act. estimations of isolated 80S ribosomes pulse-labelled with 35S-sulphate. The spec. act. have minimum values at the beginning (0.0) and maxima between 0.6 and 0.9 of the cell cycle. This pattern in spec. act. is also shown by isolated 80S ribosomes pulse-labelled with 3H-uridine during synchronous cultures and is in marked contrast to the small, random variations in the spec. act. of isolated 80S ribosomes from control, asynchronous cultures pulse-labelled with 35S-sulphate or 3H-uridine. A detailed examination of the rates of synthesis of total RNA through the cell cycle measured by the rates of incorporation of 3H-uridine and 3H-adenine shows a step in the rates of incorporation at the time of DNA synthesis. This step has further been shown to be independent both of the uridine concentration, over a range from 0.03 μM to 820 μM, and of pre-filling the adenine pool. This step thus appears to be independent of variations in rates of uptake of both purines and pyrimidines, or fluctuations in the pool size of the precursors and may be explained as a gene-dosage effect. The step in the pattern of synthesis of total RNA has been shown to yield a cyclic pattern in the spec. act. of the total RNA through the cell cycle. This pattern is similar to that of the spec, act. of RNA and of protein recovered from ribosomes. The variation exhibited by the ribosomal proteins is believed to be a consequence of the step in the pattern of RNA synthesis, with a concomitant fluctuation in the pool of ribosomal proteins synthesised continuously through the cell cycle. © 1973.