The availability of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is currently limited because they are produced mainly by marine fisheries that cannot keep pace with the demands of the growing market for these products. A sustainable non-animal source of EPA and DHA is needed. Metabolic engineering of the oleaginous yeast Yarrowia lipolytica resulted in a strain that produced EPA at 15% of dry cell weight. The engineered yeast lipid comprises EPA at 56.6% and saturated fatty acids at less than 5% by weight, which are the highest and the lowest percentages, respectively, among known EPA sources. Inactivation of the peroxisome biogenesis gene PEX10 was crucial in obtaining high EPA yields and may increase the yields of other commercially desirable lipid-related products. This technology platform enables the production of lipids with tailored fatty acid compositions and provides a sustainable source of EPA.

Oleaginous yeast Yarrowia lipolytica is an important host for the production of lipidderived compounds or heterologous proteins. Selection of strong promoters and effective expression systems is critical for heterologous protein secretion. To search for a strong promoter in Y. lipolytica, activities of FBA1, TDH1 and GPM1 promoters were compared to that of TEF1 promoter by constructing GUS reporter fusions. The FBA1 promoter activity was 2.2 and 5.5 times stronger than the TDH1 and GPM1 promoters, respectively. The FBA1 IN promoter (FBA1 sequence of À826 to +169) containing an intron (+64 to +165) showed five-fold higher expression than the FBA1 promoter (À831 to À1). The transcriptional enhancement by the 5′-region within the FBA1 gene was confirmed by GPM1::FBA1 chimeric promoter construction. Using the strong FBA1 IN promoter, four different S. cerevisiae SUC2 expression cassettes were tested for the SUC + phenotype in Y. lipolytica. Functional invertase secretion was facilitated by the Xpr2 prepro-region with an additional 13 amino acids of mature Xpr2, or by the native Suc2 signal sequence. However, these two secretory signals in tandem, or the mature Suc2 with no secretory signal, did not direct secretion of functional invertase. Unlike previously reported Y. lipolytica SUC + strains, our engineered stains secreted most of invertase into the medium. Copyright

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We characterized rice cDNA sequences for OsDr1 and OsDrAp1 , which encode structural homologs of the eukaryotic general repressors Dr1 and DrAp1, respectively. OsDr1 and OsDrAp1 are nuclear proteins that interact with each other and with the TATA binding protein/DNA complex. In vitro and in vivo functional analyses showed that OsDrAp1 functions as a repressor, unlike its role in other eukaryotic systems, in which DrAp1 is a corepressor. OsDr1 and OsDrAp1 functioned together as a much stronger repressor than either one alone. Functional dissections revealed that the N-terminal histone-fold domains of OsDr1 and OsDrAp1 were necessary and sufficient for their repression and proteinprotein interaction with each other. The unique glutamine-and proline-rich domain of OsDr1 had no repression activity. The basic amino acid-rich region and an arginine and glycine repeat domain of OsDrAp1 enhanced its repression activity. Thus, although OsDr1 and OsDrAp1 function as repressors, the functions of the two components are reversed compared with those of their nonplant counterparts. INTRODUCTIONSuccessful plant growth, development, and response to environmental cues require precise control of gene expression. A key control stage of differential gene expression is transcriptional regulation mediated by transcriptional factors. Studies of plant transcription factors have focused mainly on activators (Schwechheimer et al., 1998;Riechmann et al., 2000), whereas repressors have just begun to receive attention.Several transcriptional repressors have been cloned from plants, and the elucidation of their functional mechanisms has begun. Transcriptional repressors have been found to mediate plant hormone signal transduction. For example, the soybean G box binding factor 2 (SGBF-2) is a basic leucine zipper (bZIP)-type factor that binds to the G box of the auxin response element of the GH3 promoter and represses both basal and auxin-induced transcription of a reporter gene (Liu et al., 1997). In Arabidopsis, auxin response factor 1 (ARF1) binds to the auxin response element TGTCTC and functions as a repressor (Ulmasov et al., 1999). Arabidopsis ethylene-responsive element binding factors 3 and 4 (AtERF3 and AtERF4) interact with the ethylene-responsive element (GCC box) and repress the basal activity of a reporter gene and the activity of the transcription activator AtERF5 (Fujimoto et al., 2000). Tobacco ERF3 (NtERF3) also functions as a GCC box-dependent transcriptional repressor. The C-terminal 35 amino acids of NtERF3, which contains the conserved L/FDLNL/F(X)P motif, are sufficient to confer the capacity for transcriptional repression on a heterologous DNA binding domain (Ohta et al., 2001). A developmentspecific transcriptional repressor gene, ROM2 , has been cloned from French bean. ROM2 is a bZIP-type transcription factor that functions as a DNA binding site-dependent repressor. ROM2 represses PvALF-activated transcription of the promoter of phytohemagglutinin ( DLEC2 ). The expression analysis indicates that the ROM2 repressor m...