Purification and Partial Characterization of α‐Factor, a Mating‐Type Specific Inhibitor of Cell Reproduction from <i>Saccharomyces cerevisiae</i>

Abstract

Cells of Saccharomyces cerevisiae exhibiting the α mating type excrete into the culture medium a low‐molecular‐weight substance, termed α factor. This factor, which specifically inhibits DNA replication in cells of the opposite mating type a, has been purified more than 100000‐fold from culture filtrates of α cells. Purified α factor appears to be homogeneous as judged from thin‐layer chromatography and thin‐layer electrophoresis in different systems. It shows a positive‐ninhydrin reaction and, upon hydrolysis, gives rise to several ninhydrin‐positive substances of which the amino acids leucine, glycine, proline, glutamic acid, tyrosine, tryptophan and possibly histidine have been identified. The presence of tryptophan and tyrosine is also confirmed by the ultraviolet absorption spectrum of the factor. In addition, purified α factor contains cupric ions which can be separated from the ninhydrin‐positive material by thin‐layer electrophoresis at pH 3.6. Gel filtration on Sephadex G‐25 in 8 M urea indicates a molecular weight in the range of 1400. The properties of the purified α factor are consistent with those of a low‐molecular‐ weight peptide.