Alterations in Activity of Bacterial β-lactamase Encoded on Yeast YEp Vector with Growth

Abstract

Saccharomyces cerevisiae containing YEp vector were grown vegetatively. YEp behaves like nuclear DNA and replicates only once during S stage. Our research was aimed at elucidating functions causing the alterations in gene product content under constant dosage by monitoring activity of β-lactamase (bla) from Escherichia coli encoded on the vector. A mathematical description was made to interpret changes in the activity on the basis of the cell cycle, which suggested that the activity per cell could increase or decrease with growth independenly of copy number. We have found that the culture age of inoculum is effective in the upward or downward trend of the activity per cell in logarithmic growth. When cultures from the logarithmic growth phase were inoculated. bla activity per cell decreased with growth. Inocula from the stationary phase, where turnover of bla had progressed, caused an increase. Such trends are seemingly determined at the time of inoculation, Considering that the yields of gene product per cell are variable even under the control of the vector of constant copy number, it is difficult to estimate copy numbers from the yields of gene product.