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At least 109 records · Page 6Linked to original sources
PubMed2000

Translation initiation of a bicistronic mRNA of Borna disease virus: a 16-kDa phosphoprotein is initiated at an internal start codon.

We examined translational initiation of a bicistronic 0.8-kb mRNA of Borna disease virus (BDV) using a cDNA clone of the mRNA. Upon transfection with the clone, COS-7 cells produced a 16-kDa protein (P'), in addition to the previously identified products of BDV, 24- (P) and 14.5-kDa proteins. The 16-kDa product was detected by anti-P monoclonal antibody and was shown to exist in BDV-infected cell lines as well as in infected animal brain cells. Transient expression analysis of mutated cDNA clones encoding the BDV 0.8-kb mRNA revealed that the 16-kDa protein was initiated at the second AUG codon on the same open reading frame of the P protein. The mutational analysis also demonstrated that the first AUG within the 0.8-kb mRNA is not optimal, although the signal contains a better Kozak's motif. These results demonstrated the presence of three functional AUG codons in the smallest mRNA of BDV and also suggested that a leaky scanning mechanism is involved in translational initiation at AUG codons downstream of the bicistronic mRNA of BDV. Furthermore, the 16-kDa protein was located in the BDV-specific nuclear foci and was found to associate with the other viral proteins in BDV-infected cells, demonstrating an important role of the novel identified BDV protein in viral replication.

Amino Acid Sequence↗
PubMed1993

In-vitro translation of mitochondrial mRNAs by yeast mitochondrial ribosomes is hampered by the lack of start-codon recognition.

In an attempt to reconstitute an homologous in-vitro translation system for yeast mitochondrial mRNAs, we have isolated ribosomes, supernatant factors, and tRNAs from mitochondria of Saccharomyces carlsbergensis. While poly(U) is translated faithfully in this system, no translation of in-vitro synthesised cytochrome c oxidase subunit II (COX2) mRNA could be detected. Formation of formylmethionyl-puromycin on mitochondrial ribosomes is stimulated by ApUpG, but not by COX2 mRNA, although mitochondrial small ribosomal subunits bind to this mRNA in vitro, even without added tRNA and initiation factors. We conclude, therefore, that the inability to faithfully translate mitochondrial mRNAs in vitro may be the result of an inability of mitochondrial ribosomes to recognize the initiation codon.

Codon↗
PubMed2005

The vitamin D receptor fokI start codon polymorphism and bone mineral density in male hypogonadotrophic hypogonadism.

The genetic factors determining bone mineral density (BMD) are not well characterized. Many studies have investigated the relationship between the fokI polymorphism of vitamin D receptor (VDR) gene in diverse populations and gender, resulting in conflicting outcomes. Because peak bone mass in men is closely related to sufficient androgen release, the contribution of VDR gene on BMD might have been masked by hormonal status of adulthood. We therefore investigated the relationship between the fokI polymorphism of VDR and BMD in male patients with idiopathic hypogonadotrophic hypogonadism (IHH). Sixty-five untreated male patients with IHH and 39 healthy matched controls were evaluated. fokI polymorphism ("f" allele) was detected by polymerase chain reaction (PCR)-restriction fragment length polymorphism using restriction endonuclease fokI, and BMD was measured by dual Energy X-ray absorpsiometry in lumbar spine, femur and radius. The distribution of FF, Ff, and ff alleles in patients with IHH and controls were not different (patients; 46%, 51%, 3% and controls; 51.3%, 46.1%, 2.6%, respectively). BMD levels in patients with IHH were significantly lower than controls. We categorized patients and control subjects in subgroups according to whether they had homozygous FF and heterozygous Ff genotype. No differences in BMD were seen between control subgroups, but total femur and femoral neck BMD were significantly lower in patients bearing heterozygous Ff genotype with IHH than homozygous FF ones (p=0.017 and p=0.009, respectively). Ff genotype might run down the BMD in cortical bone of femur, which needs to be proved in further studies.

Adult↗
PubMed2004

Vitamin D receptor gene start codon polymorphism (FokI) is associated with forearm bone mineral density and calcaneal ultrasound in Finnish adolescent boys but not in girls.

We examined the association between vitamin D receptor (VDR) gene FokI polymorphism and bone mineral density and quantitative ultrasound parameters in Finnish adolescents. We assessed bone mineral density at the distal sites of radius and ulna, quantitative ultrasound of the calcaneus, serum concentration of 25-hydroxyvitamin D (25-OHD), calcium intake, physical activity, and BsmI and FokI polymorphisms of the vitamin D receptor gene in 86 girls and 38 boys aged 14 to 16 years. In girls, FokI polymorphism was not significantly associated with bone mineral density or quantitative ultrasound parameters. In adolescent boys, the Ff genotype was associated with higher forearm BMD and calcaneal ultrasound values, when adjusted for body and bone size, BsmI polymorphism, calcium intake, vitamin D status, smoking, and physical activity.

Adolescent↗
PubMed2000

Association of the vitamin D receptor start codon polymorphism (FokI) with bone mineral density in postmenopausal Korean women.

We undertook this study in order to examine the association between bone mineral density (BMD) and a polymorphism at the first of two potential translation initiation codons in the vitamin D receptor (VDR) gene. This polymorphism was detected by restriction fragment length polymorphism analysis, using polymerase chain reaction (PCR) and the restriction endonuclease FokI. The f allele indicates the presence of the FokI site, and the F allele its absence. The FokI genotype was determined in 174 postmenopausal Korean women, aged 43-71 years. The distribution of FokI genotypes in Koreans was found not to differ significantly from those found in Caucasians and Japanese, although it does differ significantly from that found in the black American population. We observed a significant association between the FokI polymorphism and lumbar BMD; P = 0.048, analysis of covariance [ANCOVA], but no association with femoral neck BMD (P = 0.505, ANCOVA). Those with the ff genotype had a 13.3% lower BMD in the lumbar spine than the FF subjects. In addition, a significantly higher prevalence of the ff genotype was observed in osteoporotic compared with osteopenic or normal women (P = 0.036, chi2 test). These data suggest that the ff genotype of the VDR gene correlates with decreased BMD in the lumbar spine in postmenopausal Korean women.

Base Sequence↗
PubMed2002

The bicistronic MOCS1 gene has alternative start codons on two mutually exclusive exons.

The bicistronic MOCS1 gene encodes two enzymatic activities that are necessary for the biosynthesis of the molybdenum cofactor (MoCo). Mutations in either of the two consecutive open reading frames are responsible for the majority of MoCo deficiency cases and result in a complementation group A phenotype. Two cDNA sequences have been described, which differ in the 5' sequence and encode for two forms of the protein MOCS1A with variable N-terminal sequences. We have reinvestigated the corresponding region by means of cDNA analysis and databank searches. This revealed three different splice variants, including two mutually exclusive first exons and a facultative intron. All three forms can be found in eight different human tissues in a constant ratio, which excludes tissue specificity of the different isoforms.

Alternative Splicing↗
PubMed1999

The vitamin D receptor FokI start codon polymorphism and bone mineral density in osteoporotic postmenopausal French women.

This study examined the association between bone mineral density (BMD) and a T/C polymorphism in the first of the two initiation codons in the vitamin D receptor (VDR) gene. The polymorphism was detected using the restriction enzyme FokI, the F allele indicating absence of the first codon and the f allele its presence. The FokI genotype was determined in 124 postmenopausal osteoporotic French women who were 45-90 years old. The distribution of FokI genotypes in the osteoporotics did not differ significantly from that found in a control group. There were no significant differences by FokI genotype groups in our total sample of osteoporotic women for age, years since menopause, height, weight, and BMD at lumbar spine and femoral neck. However, when only those patients under the age of 75 years are analysed (98 subjects), those with the ff genotype (10% of the population) had a significantly lower BMD at the femoral neck than FF and Ff subjects. This suggests that the ff genotype of the VDR gene correlates with decreased BMD at the femoral neck in French postmenopausal women.

Aged↗
PubMed2004

Choice of a start codon in a single transcript determines DNA ligase 1 isoform production and intracellular targeting in Arabidopsis thaliana.

DNA ligase 1 (AtLIG1) is the only essential DNA ligase activity in Arabidopsis and is implicated in the important processes of DNA replication, repair and recombination and in transgene insertion during Agrobacterium-mediated plant transformations. The mitochondrial and nuclear forms of DNA ligase 1 in Arabidopsis are translated from a single mRNA species through the control of translation initiation from either the first (M1) or second (M2) in-frame AUG codons respectively. Translation from a third in-frame AUG codon (M3) occurs on transcripts in which M1 and M2 are mutagenized to stop codons. Wild-type AtLIG1-GFP constructs (where GFP stands for green fluorescent protein) can be targeted in planta to both the nucleus and mitochondria. AtLIG1-GFP translation from M1 specifically targets the fusion protein only to mitochondria in planta, whereas translation from M2 or M3 targets the fusion protein only to the nucleus. Interestingly, the AtLIG1-GFP fusion protein in which translation is initiated from M1 contains both an N-terminal mtPS (mitochondrial targeting presequence) and a nuclear localization signal; nonetheless, this protein is only targeted to the mitochondria. This result raises intriguing questions on the translational control mechanisms that regulate how the protein products of a single transcript are targeted to more than one cellular compartment.

Amino Acid Sequence↗
PubMed2001

The AUG start codon of the Saccharomyces cerevisiae NFS1 gene can be substituted for by UUG without increased initiation of translation at downstream codons.

The selection of the site for initiation of translation for the Saccharomyces cerevisiae NFS1 gene was examined using mutated AUG1, AUG2 and AUG3 codons. When AUG1 of the yeast NFS1 gene was mutated to UUG and the resulting mRNA was translated in vitro using a reticulocyte system, initiation from the mutated codon was abolished and occurred instead at downstream codons at increased rates. When the same mRNA was translated using a yeast extract, translation initiated at the mutated codon, albeit at a reduced rate, and there was no increased translation at downstream AUG codons. The NFS1 gene in which AUG1 was replaced by UUG was also able to substitute for the wild-type gene in vivo in yeast. Western blots confirmed that the encoded protein was the same size as that encoded by the wild-type gene and that both the wild-type and mutated proteins localized to mitochondria. This is apparently the first example of a yeast protein where mutagenesis of AUG1 does not lead to alternate use of a downstream AUG.

Amino Acid Sequence↗
PubMed2002

Expression of the Escherichia coli pcnB gene is translationally limited using an inefficient start codon: a second chromosomal example of translation initiated at AUU.

Expression of the gene pcnB, encoding the dispensable Escherichia coli poly(A) polymerase (PAPI), which is toxic when overproduced, was investigated. Its promoter was identified and found to be moderately strong when used to express a beta-galactosidase reporter. Expression levels were not affected by increasing or decreasing PcnB concentration. Translation of pcnB was found to initiate from the non-canonical initiation codon AUU. The only other coli gene reported to use AUU as initiation codon is infC, which encodes the initiation factor IF-3. AUU, in common with other rarely used initiation codons, is discriminated against by IF-3, resulting in the aborting of most AUU-promoted initiation events. This enables AUU to form part of an autoregulatory circuit controlling IF-3 production. We show that InfC discrimination reduces PcnB production fivefold. This is the first instance of this mechanism being used to limit severely the production of a potentially toxic product.

Base Sequence↗
PubMed2004

Surprising features of plastid ndhD transcripts: addition of non-encoded nucleotides and polysome association of mRNAs with an unedited start codon.

RNA editing in higher plant plastids is a post- transcriptional RNA maturation process changing single cytidine nucleotides into uridine. In the ndhD transcript of tobacco and several other plant species, editing of an ACG codon to a standard AUG initiator codon is believed to be a prerequisite for translation. In order to test this assumption experimentally, we have analyzed the editing status of ndhD mRNA species in the process of translation. We show that unedited ndhD transcripts are also associated with polysomes in vivo, suggesting that they are translated. This surprising finding challenges the view that ACG to AUG editing is strictly required to make the ndhD message translatable and raises the possibility that ACG can be utilized as an initiator codon in chloroplasts. In addition, we have mapped the termini of the ndhD transcript and discovered a novel form of RNA processing. Unexpectedly, we find that highly specific sequences are added to the 3' end of the ndhD mRNA at high frequency. We propose a model in which these sequences are added by the successive action of a CCA-adding enzyme (tRNA nucleotidyltransferase) and an RNA-dependent RNA polymerase (RdRp) activity. The presence of an RdRp activity may have general implications also for other steps in plastid gene expression.

Base Sequence↗
PubMed2006

Translation of chloroplast psbD mRNA in Chlamydomonas is controlled by a secondary RNA structure blocking the AUG start codon.

Translation initiation represents a key step during regulation of gene expression in chloroplasts. Here, we report on the identification and characterization of three suppressor point mutations which overcome a translational defect caused by the deletion of a U-rich element in the 5'-untranslated region (5'-UTR) of the psbD mRNA in the green alga Chlamydomonas reinhardtii. All three suppressors affect a secondary RNA structure encompassing the psbD AUG initiation codon within a double-stranded region as judged by the analysis of site-directed chloroplast mutants as well as in vitro RNA mapping experiments using RNase H. In conclusion, the data suggest that these new element serves as a negative regulator which mediates a rapid shut-down of D2 synthesis.

5' Untranslated Regions↗
PubMed2005

Association between a protein polymorphism in the start codon of the vitamin D receptor gene and severe diabetic retinopathy in C-peptide-negative type 1 diabetes.

CONTEXT: The vitamin D (VD) receptor (VDR) is extensively expressed in retina. The plasma concentration of 1,25-dihydroxyvitamin D3 has been inversely correlated with the severity of diabetic retinopathy (DR), which raises the possibility that VD, through its antiinflammatory, antioxidant, antiproliferative, and antiangiogenic properties, may protect diabetic retina. The TaqI VDR polymorphism has been associated with severe DR. The FokI VDR polymorphism is a T-to-C substitution in the first codon (f allele), abolishing the first translation initiation site and resulting in a peptide lacking three amino acids (F allele), which increases the transcriptional activity of VDR. OBJECTIVE AND DESIGN: To examine whether FokI polymorphism is involved in severe DR, 254 Caucasians with longstanding C-peptide-negative type 1 diabetes, 128 patients with absent/mild DR (control group), and 126 patients with preproliferative/proliferative DR (study group) were genotyped using PCR-restriction fragment length polymorphism analysis. RESULTS: The genotype distribution was in Hardy-Weinberg equilibrium and was different between groups (P = 0.046). The frequency of F allele was significantly higher in the control (66.4%) than in the study group (56%, odds ratio = 0.64, 95% confidence interval 0.44-0.92, P = 0.016). In subjects with fewer than 25 yr of diabetes duration (median value, n = 134), this association was strongly increased (P = 0.0008). CONCLUSIONS: In conclusion, we observed, in a cohort of Caucasians with C-peptide-negative type 1 diabetes, a novel association between the functional FokI VDR polymorphism and severe DR, especially among subjects with fewer than 25 yr of diabetes duration.

Adult↗
PubMed1999

The vitamin D receptor (VDR) start codon polymorphism in primary hyperparathyroidism and parathyroid VDR messenger ribonucleic acid levels.

Vitamin D regulates parathyroid cell proliferation and secretion of PTH. Increased prevalence of the polymorphic vitamin D receptor (VDR) alleles b, a, and T has been reported in sporadic primary hyperparathyroidism (PHPT), suggesting that these genetic variants may predispose to the disease. Recently, another polymorphism in the VDR gene was related to bone mineral density, and this VDR-FokI polymorphism causes different lengths of the VDR, implying possible functional consequences. The VDR-FokI polymorphism was studied in 182 postmenopausal women with sporadic PHPT and in matched controls. No significant differences in distribution of the VDR-FokI genotypes could be detected between the groups, although there was a tendency toward overrepresentation of the F allele in the PHPT patients (P = 0.05). There were no significant associations with age, serum calcium, serum PTH, bone mineral density, or parathyroid tumor weight. The VDR genotypes were unrelated to VDR and PTH messenger ribonucleic acid levels in the parathyroid adenomas of 42 PHPT patients. In 23 PHPT patients, the Ca2+-PTH set-points were determined in vivo and were unrelated to the VDR alleles. We suggest that the VDR-FokI polymorphism has at most a minor pathogenic importance in the development of PHPT.

Adult↗