Alex B Lopez

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Despite recent progress in our understanding of carotenogenesis in plants, the mechanisms that govern overall carotenoid accumulation remain largely unknown. The Orange (Or) gene mutation in cauliflower (Brassica oleracea var botrytis) confers the accumulation of high levels of beta-carotene in various tissues normally devoid of carotenoids. Using(More)
It was previously shown that the mRNA for the cat-1 Arg/Lys transporter is translated from an internal ribosome entry site (IRES) that is regulated by cellular stress. Amino acid starvation stimulated cat-1 translation via a mechanism that requires translation of an ORF in the mRNA leader and remodeling of the leader to form an active IRES (the "zipper(More)
Phytoene desaturase (PDS; EC 1.14.99.-) represents one of the key enzymes in the carotenoid biosynthetic pathway and is present in nearly all types of plastids in plants. To further characterize PDS, we isolated the PDS cDNA from cauliflower (BoPDS) and confirmed its function by heterologous expression in a strain of Escherichia coli containing a(More)
The SerH locus of Tetrahymena thermophila is one of several paralogous loci with genes encoding variants of the major cell surface protein known as the immobilization antigen (i-ag). The locus is highly polymorphic, raising questions concerning functional equivalency and selective forces acting on its multiple alleles. Here, we compare the sequences and(More)
The cyst wall of Giardia intestinalis contains proteins and a novel N-acetylgalactosamine (GalNAc) polysaccharide, which is its major constituent. GalNAc is not present in growing trophozoites, but is synthesized during encystment via an inducible pathway of enzymes that produce UDP-GalNAc from fructose 6-phosphate. This report focuses on the regulation of(More)
Cells respond to physiological stress by phosphorylating the alpha subunit of the translation initiation factor eIF2. This adaptive response inhibits protein synthesis and up-regulates genes essential for cell survival. Cat-1, the transporter for the essential amino acids, arginine and lysine, is one of the up-regulated genes. We previously showed that(More)
The cyst wall of the parasitic protozoan, Giardia intestinalis, is composed of a polymer of N-acetylgalactosamine, the precursor of which is synthesized by an inducible enzyme pathway. The first enzyme in this pathway, glucosamine 6-phosphate isomerase, is transcriptionally regulated. During encystment and in mature cysts this isomerase appears to be(More)
The adaptive response to amino acid limitation in mammalian cells inhibits global protein synthesis and promotes the expression of proteins that protect cells from stress. The arginine/lysine transporter, cat-1, is induced during amino acid starvation by transcriptional and post-transcriptional mechanisms. It is shown in the present study that the transient(More)
Expression of the Cat-1 gene (cationic amino acid transporter-1) is induced in proliferating cells and in response to a variety of stress conditions. The expression of the gene is mediated via a TATA-less promoter. In the present study we show that an Sp1 (specificity protein 1)-binding site within a GC-rich region of the Cat-1 gene controls its basal(More)
The protozoan parasite Giardia intestinalis has a simple life cycle consisting of an intestinal trophozoite stage and an environmentally resistant cyst stage. The cyst is formed when a trophozoite encases itself within an external filamentous covering, the cyst wall, which is crucial to the cyst's survival outside of the host. The filaments in the cyst wall(More)