SYNTHESIS AND MODIFICATION OF PROTEINS DURING THE CELL-CYCLE OF THE YEAST SACCHAROMYCES-CEREVISIAE

A novel technique was used to study the synthesis, modification and degradation of proteins during the cell cycle in S. cerevisiae. Logarithmically growing cells were pulse-labeled twice, with the pulses separated in time by more than 1 generation. The cells were then fractionated as to their position in the cell cycle by centrifugal elutriation and for different proteins the ratio of radioactive material from the 2 pulses was determined. Periodic degradation, synthesis or modification would produce periodic variations in the ratio of counts. Two-dimensional gel electrophoresis was used to examine 110 different proteins at different times of the cell cycle. All but 2 proteins had a constant ratio of counts through the cell cycle. Apparently the rate of synthesis of individual proteins increases exponentially during the cell cycle and periodic degradation or modification of proteins is not a general feature of the cell cycle in S. cerevisiae.