Effect of p H on Adenine and Amino Acid Uptake During Sporulation in Saccharomyces cerevisiae

Abstract

During the early stages of sporulation in Saccharomyces cerevisiae , the p H of the acetate sporulation medium rises to values of 8.0 or higher. Associated with this rise in p H is a reduced cell permeability to certain precursors of ribonucleic acid (RNA), deoxyribonucleic acid or protein. Uptake of adenine, alanine, and leucine was optimal at p H 5.6 to 6.0, but sporulation was inhibited when the sporulation medium was buffered below p H 7.0. Cellular impermeability can be largely overcome by adjusting the acetate sporulation medium to p H 6.0 for optimal uptake of ¹⁴ C-adenine during short pulses without any apparent effect on sporulation. Sporulating cells pulse-labeled 20 min at p H 6.0 incorporated 40 times more ¹⁴ C-adenine into RNA than sporulating cells pulse-labeled at p H 8.0. This increased incorporation can be attributed to a 100-fold increase in labeled adenosine triphosphate in cells pulse-labeled at p H 6.0 where maximum uptake occurs.