Put3 Positively Regulates Proline Utilization in .

The zinc cluster transcription factor Put3 was initially characterized in as the transcriptional activator of and , two genes acting early in the proline assimilation pathway. We have used phenotypic studies, transcription profiling, and chromatin immunoprecipitation with microarray technology (ChIP-chip) to establish that unlike , which only uses proline as a nitrogen source, can use proline as a nitrogen source, a carbon source, or a source of both nitrogen and carbon. However, a null mutant cannot grow on proline, suggesting that as in , Put3 (CaPut3) is required for proline catabolism, and because the null mutant grew efficiently on glutamate as the sole carbon or nitrogen source, it appears that CaPut3 also regulates the early genes of the pathway. CaPut3 showed direct binding to the promoter, and both and were upregulated in response to proline addition in a Put3-dependent manner, as well as in a strain expressing a hyperactive Put3. CaPut3 directs proline degradation even in the presence of a good nitrogen source such as ammonia, which contrasts with Put3 (ScPut3)-regulated proline catabolism, which only occurs in the absence of a rich nitrogen source. Thus, while overall proline regulatory circuitry differs between and , the specific role of Put3 appears fundamentally conserved. poses a significant threat to the lives of immunocompromised people. Historically, knowledge has been drawn from studies on to understand the pathogen, and many genes are named after their orthologs. Direct studies on the pathogen have, however, revealed differences in the roles of some orthologous proteins in the two yeasts. We show that the Put3 transcription factor allows the pathogen to completely degrade proline to usable nitrogen and carbon by evading regulatory restrictions imposed on its ortholog, which mandates conditional use of proline only as a nitrogen source in the baker's yeast. The ability of to freely obtain nutrients from multiple sources may help it thrive as a commensal and opportunistic pathogen.