Yeast Saccharomyces cerevisiae can utilize proline as a single nitrogen source. We have found that the strains with mutations in gene PH085, a structural gene encoding cyclin-dependent phosphoprotein kinase, cannot grow on the proline-containing media. The ability to utilize proline is restored in strains of the pho85pho4 genotype. We suggest that phosphoprotein kinase Pho85p is involved in either phosphorylation of a highly specific proline permease, Put4p, or in signaling proline concentration. The Pho4p protein that activates transcription of the PH05 gene, a structural gene of acid phosphatase, seems to participate in the negative regulation of the PUT1 and PUT2 genes encoding enzymes of proline catabolism, proline oxidase and delta-pyrroline-5-carboxylate dehydrogenase. Thus, regulation of phosphorus and nitrogen metabolism have common elements.