Disease resistance in transgenic plants has been improved, for the first time, by the insertion of a gene from a biocontrol fungus. The gene encoding a strongly antifungal endochitinase from the mycoparasitic fungus Trichoderma harzianum was transferred to tobacco and potato. High expression levels of the fungal gene were obtained in different plant tissues, which had no visible effect on plant growth and development. Substantial differences in endochitinase activity were detected among transformants. Selected transgenic lines were highly tolerant or completely resistant to the foliar pathogens Alternaria alternata , A. solani , Botrytis cinerea , and the soilborne pathogen Rhizoctonia solani . The high level and the broad spectrum of resistance obtained with a single chitinase gene from Trichoderma overcome the limited efficacy of transgenic expression in plants of chitinase genes from plants and bacteria. These results demonstrate a rich source of genes from biocontrol fungi that can be used to control diseases in plants.

We have isolated a human cDNA clone encoding a novel protein of 22 kDa that is a human counterpart of the rat oncoprotein PTTG. We show that the corresponding gene (hpttg) is overexpressed in Jurkat cells (a human T lymphoma cell line) and in samples from patients with di erent kinds of hematopoietic malignancies. Analysis of the sequence showed that hPTTG has an aminoterminal basic domain and a carboxyl-terminal acidic domain, and that it is a proline-rich protein with several putative SH3-binding sites. Subcellular fractionation studies show that, although hPTTG is mainly a cytosolic protein, it is partially localized in the nucleus. In addition we demonstrate that the acidic carboxyl-terminal region of hPTTG acts as a transactivation domain when fused to a heterologous DNA binding domain, both in yeast and in mammalian cells.

The gene PTTG1 (encoding the pituitary tumor-transforming 1 protein) is overexpressed in several different tumor types, is tumorigenic in vivo and shows transcriptional activity. The PTTG1 protein is cell-cycle regulated and was identified as the human securin (a category of proteins involved in the regulation of sister-chromatid separation) on the basis of biochemical similarities with the Pds1p protein of budding yeast and the Cut2p protein of fission yeast. To unravel the function of human securin in oncogenesis, we carried out a phage-display screening to identify proteins that interact with securin. Notably, we isolated the p53 tumor suppressor. Pull-down and co-immunoprecipitation assays demonstrated that p53 interacts specifically with securin both in vitro and in vivo. This interaction blocks the specific binding of p53 to DNA and inhibits its transcriptional activity. Securin also inhibits the ability of p53 to induce cell death. Moreover, we observed that transfection of H1299 cells with securin induced an accumulation of G2 cells that compensated for the loss of G2 cells caused by transfection with p53. We demonstrated the physiological relevance of this interaction in PTTG1-deficient human tumor cells (PTTG1(-/-)): both apoptotic and transactivating functions of p53 were potentiated in these cells compared to parental cells. We propose that the oncogenic effect of increased expression of securin may result from modulation of p53 functions.

We recently isolated a cDNA for hpttg, the human homolog of rat pituitary tumor transforming gene. Now we have analysed the expression of hpttg as a function of cell proliferation. hPTTG protein level is up-regulated in rapidly proliferating cells, is down-regulated in response to serum starvation or cell con¯uence, and is regulated in a cell cycle-dependent manner, peaking in mitosis. In addition, we show that hPTTG is phosphorylated during mitosis. Immunodepletion and in vitro phosphorylation experiments, together with the use of a speci®c inhibitor, indicate that Cdc2 is the kinase that phosphorylates hPTTG. These results suggest that hpttg is induced by, and may have a role in, regulatory pathways involved in the control of cell proliferation. Oncogene (2000) 19, 403 ± 409.