Growth and changes in pool and macromolecular components of Schizosaccharomyces pombe during the cell cycle.

Abstract

ABSTRACT Amino acids, nucleotide and carbohydrate material were found to account for 46 % of the total dry weight of pool material in Schizosaccharomyces pombe growing in minimal medium. The composition of the amino acid pool was also determined by autoanalysis and was found to be unaltered during growth in 2 M sorbitol, indicating that pool amino acids are not important in the osmoregulation of the cell. Kinetic analysis of the amino acid pool using 14C-labelled amino acids showed that amino acids accumulated from the medium enter an ‘expandable’ pool distinct from the ‘internal ‘pool which is maintained during growth on minimal medium. Total RNA, protein, pool amino acid and pool ‘nucleotide’ material were estimated in synchronous cultures grown in minimal medium. All these components appeared to accumulate in an exponential manner during the cell cycle. Direct estimation of total cellular dry weight and the total pool in synchronous cultures showed that total cell dry weight increased exponentially and the pool did not fluctuate during growth in minimal medium. This contrasts with previous work on single cells of S. pombe grown in complex medium which showed that the dry weight of the pool fluctuates during the cell cycle and total cell dry weight increased linearly. Linear growth of S. pombe in malt extract broth can be accounted for by the presence of the second (‘expandable ‘) pool of amino acids formed during growth in complex medium. The phenomenon of linear growth during the cell cycle is shown to occur generally only in cells growing in complex medium. The phenomenon is considered in relation to mechanisms for controlling the size of the pool during growth in complex media.