The enzyme 3-hydroxy-3-methylglutarylCoA reductase (HMGR; EC 1.1.1.34) catalyzes the first ratelimiting step in plant isoprenoid biosynthesis. Arabidopsis thaliana contains two genes, HMGI and HMG2, that encode HMGR. We have doned these two genes and analyzed their structure and expression. HMGI and HMG2 consist of four exons and three small introns that interrupt the coding sequence at equivalent positions. The two genes share sequence similarity in the coding regions but not in the 5'-or 3'-flanking regions. HMG1 mRNA is detected in all tissues, whereas the presence of HMG2 mRNA is restricted to young seedlings, roots, and inflorescences. The similarity between the two encoded proteins (HMGR1 and HMGR2) is restricted to the regions corresponding to the membrane and the catalytic domains. Arabidopsis HMGR2 represents a divergent form of the enzyme that has no counterpart among plant HMGRs characterized so far. By using a coupled in vitro transcriptiontranslation assay, we show that both HMGR1 and HMGR2 are cotranslationally inserted into endoplasmic reticulum-derived microsomal membranes. Our results suggest that the endoplasmic reticulum is the only cell compartment for the targeting of HMGR in Arabidopsis and support the hypothesis that in higher plants the formation of mevalonate occurs solely in the cytosol.

M o n t s e r r a t Enjuto,' Victoria Lumbreras, Carles Marín, a n d A l b e r t B o r o n a t 2 Unitat de Bioquímica i Biologia Molecular A, Departament de Bioquímica i Fisiologia, Facultat de Química, Universitat de Barcelona, 08028 Barcelona, SpainThe synthesis of mevalonate, which is considered the first rate-limiting step in isoprenoid biosynthesis, is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC 1.1.1.34). In Arabidopsis, HMGR is encoded by two differentially expressed genes (HMG1 and HMGP). The transcriptional activity of the HMGP gene was studied after fusing different regions of its 5' flanking region to the P-glucuronidase (GUS) reporter gene and transforming the resulting constructs into tobacco plants. The spatial and temporal expression directed by the HMGP promoter in the transgenic plants is consistent with the expression pattern previously established by RNA analysis using an HMGBspecific probe. HMGP expression is restricted to meristematic (root tip and shoot apex) and floral (secretory zone of the stigma, mature pollen grains, gynoecium vascular tissue, and fertilized ovules) tissues. Deletion analysis of the HMGP 5'flanking region was conducted in transgenic plants and transfected protoplasts. The region containing nucleotides -857 to +64 of the HMGP gene was sufficient to confer high levels of expression in both floral and meristematic tissues, although deletion to nucleotide -503 resulted in almost complete loss of expression. Sequences contained within the 5' transcribed, untranslated region are also important for gene expression. The biological significance of the restricted pattern of expression of HMGP is also discussed.

Abstract-A functional genetic variant consisting of a C825T substitution in the GNB3 gene, encoding for the G-protein ␤ 3 subunit, has been associated with enhanced G-protein activation and cell growth. The aim of the study was to investigate the association of this polymorphism with left ventricular hypertrophy (LVH) in a sample of patients with essential hypertension. Left ventricular mass was assessed by 2-mode echocardiography in 86 patients with essential hypertension, and GNB3 C825T genotype was determined by polymerase chain reaction and restriction digestion. Thirty-seven (0.43) patients were homozygous for the C allele (CC), 40 (0.47) were heterozygous (CT), and 9 (0.10) were homozygous for the T allele (

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The Arabidopsis thaliana K + channel AKT1 was expressed in decreased K + content, and lower growth rate, as compared to control cells expressing the wild-type channel) were selected. a yeast strain defective for K + uptake at low K + concentrations ( B 3 mM). Besides restoring K + transport in this By co-expressing them with the wild-type AKT1 cDNA, it was strain, AKT1 expression increased its tolerance to salt (NaCl shown that the mutated polypeptides were expressed, stable and correctly targeted to the cell membrane where they or LiCl), whatever the external K + concentration used (50 mM, 5 mM, or 50 mM). We took advantage of the latter formed channels with altered properties. Analysis of the mutaphenomenon for screening a library of channels randomly tion distribution in these channels suggests that the AKT1 P mutated in the region that shares homologies with the pore domain has a structure similar to that of animal Shaker channels (a strongly constrained central region lining the forming domain (the so-called P domain) of animal K + tunnel that includes the highly conserved consensus motif channels (Shaker family). Cassette mutagenesis was performed using a degenerate oligonucleotide that was designed TXXTXGYGD, and flanking regions forming the outer mouth of the pore), with an additional selectivity filter located up-to ensure, theoretically, a single mutation per P cassette. The mean number of amino acid exchanges per cassette turned out stream from the tunnel and formed by residues present in the to be 1.4. Mutant channels that conferred on the transformed N-terminal flanking region. cells a reduction in salt tolerance (increased Na + content,

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The synthesis of mevalonate, which is considered the first rate-limiting step in isoprenoid biosynthesis, is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC 1.1.1.34). In Arabidopsis, HMGR is encoded by two differentially expressed genes (HMG1 and HMG2). The transcriptional activity of the HMG2 gene was studied after fusing different regions of its 5' flanking region to the beta-glucuronidase (GUS) reporter gene and transforming the resulting constructs into tobacco plants. The spatial and temporal expression directed by the HMG2 promoter in the transgenic plants is consistent with the expression pattern previously established by RNA analysis using an HMG2-specific probe. HMG2 expression is restricted to meristematic (root tip and shoot apex) and floral (secretory zone of the stigma, mature pollen grains, gynoecium vascular tissue, and fertilized ovules) tissues. Deletion analysis of the HMG2 5' flanking region was conducted in transgenic plants and transfected protoplasts. The region containing nucleotides -857 to +64 of the HMG2 gene was sufficient to confer high levels of expression in both floral and meristematic tissues, although deletion to nucleotide -503 resulted in almost complete loss of expression. Sequences contained within the 5' transcribed, untranslated region are also important for gene expression. The biological significance of the restricted pattern of expression of HMG2 is also discussed.