Naslov
Evidence for a complex regulation of Pho4 action in S. cerevisiae

Autori
Korica, Tamara ; Gregory, Philip D. ; Horz, Wolfram ; Barbarić, Slobodan

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Godišnji sastanak hrvatskih biokemičara, 1998 / Glavaš-Obrovac, Ljubica - Zagreb : Farmaceutsko-biokemijski fakultet Sveučilišta u Zagrebu, 1998, 93-93

Skup
Godišnji sastanak hrvatskih biokemičara

Mjesto i datum
Bizovačke Toplice, Hrvatska, 17.09.1994. - 20.09.1994

Vrsta sudjelovanja
Poster

Vrsta recenzije
Domaća recenzija

Ključne riječi
transcriptional regulation; PHO5; Pho4; Saccharomyces cerevisiae

Sažetak
Transcriptional activation of the yeast PHO5 promoter upon phosphate starvation requires two transcriptional activators, the bHLH protein Pho4 and the homeodomain protein Pho2. The two proteins bind to the promoter in a cooperative manner. Cooperativity requires DNA binding of both proteins as well as specific Pho2-Pho4 interaction. The activity of Pho4 is regulated through phosphorylation by Pho80-Pho85, a cyclin-cdk complex. Under repressing conditions Pho4 is phosphorylated and located predominantly in the cytoplasm. However, although non-phosphorylatable Pho4 derivatives are constitutively localised in the nucleus, activity of PHO5 in a strain expressing such mutants still increases 4 times upon induction, showing that there is yet another mechanism regulating PHO5 expression which is independent of Pho80-Pho85. In addition to six Pho85 consensus target sites, Pho4 contains two putative PKA phosphorylation sites, one being located in the basic region (Ser 254), which is involved in interactions with Pho2. We have therefore examined the possible role of Ser254 phosphorylation in the regulation of Pho4-Pho2 interactions and consequently the ability of Pho4 to bind DNA and activate transcription. To this end, we introduced two mutations into Pho4 at this residue (S254A and S254D). Expression of PHO5 in a strain containing the Pho4 derivative (S254A) was 2-3 times higher at repressive conditions than with wt Pho4, but only slightly higher at induced conditions. On the other hand, the S254D mutation, which mimicks constitutively phosphorylated Ser254, was without a significant effect at repressive conditions, but results in more than 2-fold lower activation at induced conditions, indicating that phosphorylation of Ser254 is involved in the regulation of Pho4 activity. Experiments testing the ability of the mutant Pho4 proteins to interact with Pho2 and to bind DNA are in progress.

Izvorni jezik
Engleski

Znanstvena područja
Prehrambena tehnologija

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