The present invention relates to a stabilized proline transporter Put4 obtained by gene mutation and a gene encoding the same, as well as a Saccharomyces yeast strain which is obtained by yeast transformation with the gene and is capable of efficiently using proline in a source material such as wort. The stabilized mutated proline transporter Put4 can be used to achieve efficient use of nitrogen sources such as poorly assimilable proline contained in source materials (e.g., wort) for alcohol beverages. Fermentation using yeast capable of taking up a wide variety and large amounts of nitrogen sources facilitates carbon source assimilation and allows improvement of productivity for alcohol beverages. Moreover, the use of poorly assimilable nitrogen sources leads to resource savings and enables environmentally friendly production of alcohol beverages.