Nutrient Availability and the RAS/Cyclic AMP Pathway Both Induce Expression of Ribosomal Protein Genes in Saccharomyces cerevisiae but by Different Mechanisms

Abstract

By differential hybridization, we identified a number of genes in Saccharomyces cerevisiae that are activated by addition of cyclic AMP (cAMP) to cAMP-depleted cells. A majority, but not all, of these genes encode ribosomal proteins. While expression of these genes is also induced by addition of the appropriate nutrient to cells starved for a nitrogen source or for a sulfur source, the pathway for nutrient activation of ribosomal protein gene transcription is distinct from that of cAMP activation: (i) cAMP-mediated transcriptional activation was blocked by prior addition of an inhibitor of protein synthesis whereas nutrient-mediated activation was not, and (ii) cAMP-mediated induction of expression occurred through transcriptional activation whereas nutrient-mediated induction was predominantly a posttranscriptional response. Transcriptional activation of the ribosomal protein gene RPL16A by cAMP is mediated through a upstream activation sequence element consisting of a pair of RAP1 binding sites and sequences between them, suggesting that RAP1 participates in the cAMP activation process. Since RAP1 protein decays during starvation for cAMP, regulation of ribosomal protein genes under these conditions may directly relate to RAP1 protein availability. These results define additional critical targets of the cAMP-dependent protein kinase, suggest a mechanism to couple ribosome production to the metabolic activity of the cell, and emphasize that nutrient regulation is independent of the RAS/cAMP pathway.

Transcriptional Elements Involved in the Repression of Ribosomal Protein Synthesis

“…This is true of responses to heat shock (11,24), to a defect in the secretory pathway (34 and this paper), to growth conditions such as C source (16,22), to levels of cAMP (25,39), and to the deprivation of amino acids (37,62). During the growth cycle, RP genes are repressed as the cells enter late log phase (6,21) and are induced dramatically within 10 min after stationary cells are diluted into a fresh medium (unpublished data).…”

“…4A) resembles the promoters of most RP genes, with two Rap1p binding sites as the major UAS, and one or two T-rich regions which have some promoter activity (41,45,47), followed by a less well defined region that contains the putative TATA box. Previous work has implicated the Rap1p binding sites as the elements mediating the regulation of transcription, in the response to a carbon source shift (7,16), to amino acid starvation (37), and to cyclic AMP (cAMP) (25,39), but not in the response to a temperature shift (41,45).…”

“…It has been reported that Rap1p is degraded in cells depleted of cAMP (39), resulting in the reduced transcription of RP genes. To determine if limiting Rap1p lies behind the repression of RP transcription in response to a defect in the secretory pathway, we overexpressed Rap1p in both W303 and 169ts, by transforming each strain with a 2 m plasmid carrying wt RAP1.…”

Remodeling of Yeast Genome Expression in Response to Environmental Changes

“…The protein kinase A and TOR kinase pathways are also involved in the response to nutritional signals, consistent with our observation that nearly 40% of the genes affected by nutrient limitation at the diauxic shift are also CER genes. These pathways appear to play roles in regulation of both the CER-induced and -repressed genes, via a variety of mechanisms (Klein and Struhl, 1994;Neuman-Silberg et al, 1995;Boy-Marcotte et al, 1998;Gö rner et al, 1998;Smith et al, 1998;Beck and Hall, 1999).…”

Sfp1 is a stress- and nutrient-sensitive regulator of ribosomal protein gene expression

“…The cAMP͞PKA pathway has also been shown to influence RP gene transcription in response to nutrient and carbon availability (34)(35)(36). cAMP causes activation of PKA by binding to the regulatory subunit Bcy1, triggering release and activation of the PKA catalytic subunits (37).…”