Repression of transcription by HoxC11 upon phorbol ester stimulation.

Hox genes encode transcription factors with a conserved DNA-binding domain and exhibit similar DNA-binding preferences. The in vivo specificity required for their biological function is brought about by combinatorial interactions with other factors. Such interactions also modulate their activation state. Here we show that HoxC11 can either activate or repress transcription in a signal-specific manner. We report the isolation of HoxC11 in a yeast one-hybrid screen for factors binding to a phorbol-ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) response element (VLTRE), which is also a target for TPA-induced binding of Rel factors in gel-shift experiments. Although we detect no binding of in vitro translated HoxC11 to the TPA response element in EMSA, overexpression of HoxC11 in the HepG2 cell line leads to a complete block of TPA-induced transcription from a VLTRE-luciferase reporter. There is, however, no repression of the basal levels. The repression is furthermore not dependent on homeo-domain DNA binding. Our data suggest an interaction of HoxC11 with the basal-transcription machinery. We propose that HoxC11 is capable of mediating transcriptional activation or repression in a signal-specific manner and that its activation of the DNA target sequence in yeast might reflect in vivo recruitment to the promoter complex.

Analysis of PFK3--a gene involved in particulate phosphofructokinase synthesis reveals additional functions of TPS2 in Saccharomyces cerevisiae.

The pfk3 mutation of Saccharomyces cerevisiae causes glucose-negativity in a pfk1 genetic background, the mutant is temperature-sensitive for growth and homozygous diploids do not sporulate. It fails to accumulate trehalose, and has an altered glycogen accumulation profile under glucose-starvation conditions. pfk3-6, one of the alleles of pfk3, has an altered morphology, forming long chain-like structures at 36 degrees C. The PFK3 gene was cloned by complementation of the mutant phenotypes. Integrative transformation demonstrated that the complementing fragment encoded the authentic PFK3 gene. The disruption of the gene does not affect viability. Like the EMS-induced pfk3 mutant, the disruptants are temperature-sensitive and in a pfk1 genetic background are also glucose-negative. The PFK3 transcript is induced by heat-shock. Partial DNA sequence shows that PFK3 is identical to TPS2 (De Virgilio et al., 1993). We demonstrate that, apart from being a structural determinant of trehalose 6-phosphate phosphatase, PFK3 (TPS2) is required for PFKII synthesis and normal regulation of S. cerevisiae response to nutrient and thermal stresses.