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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