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PubMed2004

The case for nuclear translation.

Although it is frequently assumed that translation does not occur in eukaryotic nuclei, recent evidence suggests that some translation can take place and that it is closely coupled to transcription. The first evidence concerns the destruction of nuclear mRNAs containing premature termination codons by nonsense-mediated decay (NMD). Only ribosomes can detect termination codons, and as some NMD occurs within the nuclear fraction, active nuclear ribosomes could perform the required detection. The second evidence is the demonstration that tagged amino acids are incorporated into nascent polypeptides in a nuclear process coupled to transcription. The third evidence is that components involved in translation, NMD and transcription colocalize, coimmunoprecipitate and co-purify. All these results are simply explained if nuclear ribosomes scan nascent transcripts for premature termination codons at the site of transcription. Alternatively, the scanning needed for NMD might take place at the nuclear membrane, and contaminating cytoplasmic ribosomes might give the appearance of some nuclear translation. We argue, however, that the balance of evidence favours bona fide nuclear translation.

Animals↗
PubMed2006

Human alpha2-globin nonsense-mediated mRNA decay induced by a novel alpha-thalassaemia frameshift mutation at codon 22.

We describe a novel alpha-thalassaemia determinant in a 3-year-old girl presenting a mild microcytic and hypochromic anaemia, and normal haemoglobin A2 level. Molecular studies revealed heterozygosity for a novel microdeletion (-C) at codon 22 of the alpha2-globin gene. As the frameshift mutation generates a premature translation termination codon at position 48/49, we investigated the effect of the nonsense codon on the alpha2-globin gene expression. Although it does not affect RNA splicing, the premature nonsense codon induces accelerated mRNA degradation. To our knowledge, this is the first time the nonsense-mediated mRNA decay has been reported to occur in human alpha-globin mRNA.

Codon, Nonsense↗
PubMed2004

Autosomal-dominant pseudohypoaldosteronism type 1 in a Turkish family is associated with a novel nonsense mutation in the human mineralocorticoid receptor gene.

Pseudohypoaldosteronism type 1 (PHA1) is a rare congenital disease inherited in either an autosomal-recessive or an autosomal-dominant trait. The autosomal-dominant form manifests with renal salt loss in infancy and a gradual improvement with advancing age. PHA1 presents with potential life-threatening salt wasting and failure to thrive in early infancy. Autosomal-dominant forms of PHA1 are often caused by heterozygous mutations of the MR gene coding for the mineralocorticoid receptor. Whether heterozygous mutations of the MR gene impair biological function as a result of haplo-insufficiency or due to a dominant-negative effect needs further clarification. We report a case of a renal form of PHA1 in a Turkish family. A heterozygous nonsense mutation c3055C>T (R947X) in exon 9 of the MR gene leading to a premature stop codon was identified in the index patient. The truncated receptor is free of aldosterone binding. The segregation analysis revealed the identical mutation in the patient's father, who never showed any symptoms of PHA. This shows the incomplete penetrance of the phenotype, although a mild salt loss might have been overlooked in the father's childhood.

Base Sequence↗
PubMed2004

Messenger RNA transcripts of the hepatocyte nuclear factor-1alpha gene containing premature termination codons are subject to nonsense-mediated decay.

Mutations in the hepatocyte nuclear factor-1alpha (HNF-1a) gene cause maturity-onset diabetes of the young (MODY). Approximately 30% of these mutations generate mRNA transcripts harboring premature termination codons (PTCs). Degradation of such transcripts by the nonsense-mediated decay (NMD) pathway has been reported for many genes. To determine whether PTC mutant transcripts of the HNF-1alpha gene elicit NMD, we have developed a novel quantitative RT-PCR assay. We performed quantification of ectopically expressed mutant transcripts relative to normal transcripts in lymphoblastoid cell lines using a coding single nucleotide polymorphism (cSNP) as a marker. The nonsense mutations R171X, I414G415ATCG-->CCA, and P291fsinsC showed reduced mutant mRNA expression to 40% (P = 0.009), <0.01% (P </= 0.0001), and 6% (P = 0.001), respectively, of the normal allele. Transcript levels were restored using the translation inhibitor cycloheximide, indicating that the instability arises from NMD. The missense mutations G207D and R229P did not show NMD although R229P exhibited moderate RNA instability. This study provides the first evidence that HNF-1alpha PTC mutations may be subject to NMD. Mutations that result in significant reduction of protein levels due to NMD will not have dominant-negative activity in vivo. Haploinsufficiency is therefore likely to be the most important mutational mechanism of HNF-1alpha mutations causing MODY.

Amino Acid Substitution↗
PubMed1992

Bipartite organization of the Bacillus subtilis endo-beta-1,4-glucanase revealed by C-terminal mutations.

The C-terminal boundary of primary sequence of the Bacillus subtilis PAP115 endo-beta-1,4-glucanase (EG) required for stable catalytic activity has been mapped by site-directed mutagenesis using Escherichia coli as host. The 52 kDa cel gene product, EG470 and a 33 kDa mutant (EG300), lacking 170 residues through a nonsense mutation at the leucine-330 codon of the gene, exhibited similar patterns of enzymatic activity and pH optima using cellooligopentaose as substrate. CD spectra indicated that the bulk of the alpha-helical secondary structure in EG470 was contained within EG300. However, relative to EG470, the specific activity of EG300 was 3- to 4-fold lower with amorphous cellulose as substrate and approximately 4- to 5-fold higher with carboxymethylcellulose (soluble cellulose). These results along with data which show that EG470 binding capacity to microcrystalline cellulose is approximately 11 times more than that of EG300, demonstrate the importance of residues 330-499 for non-catalytic binding of cellulose. A construct of the cel gene carrying a deletion of codons 330-499 and an insertion of a nonsense codon at leucine-330, was further used to make mutants EG296 and EG291 with nonsense codon substitutions at arginine-326 and serine-321, respectively. Western analysis using EG-specific antiserum revealed that relative losses in enzymatic activity of EG296 (50%) and EG291 (95%) could be accounted for by the extent of their proteolysis, signifying a marked destabilization of these enzymes by removal of only a few amino acids.

Bacillus subtilis↗
PubMed1996

Mutations in the BRCA1 gene in Japanese breast cancer patients.

Predisposing germline mutations in the BRCA1 gene were identified recently in families with 17 q-linked breast and ovarian cancers. Using single-strand conformation polymorphism (SSCP) analysis, we examined primary breast cancers for mutations in coding exons of BRCA1 in a panel of 103 patients, of whom all either represented early-onset cases (< 35 of age), were members of multiply-affected families, and/or had developed bilateral breast cancers. Mutations were detected in tumors from four patients, all of whom had developed breast cancers bilaterally: a frame-shift due to a 2-bp deletion at codon 797; a nonsense mutation at codon 1214; and two missense mutations, one at codon 271 leading to Val-->Met substitution, and the other at codon 1150 leading to Pro-->Ser substitution. In each case the same mutation was present in constitutional DNA. The mean age of onset was 49 years among the Japanese carriers of BRCA1 mutations identified in this study, in contrast to the mean age of 35 observed among carriers of BRCA1 mutations in a similar U.S. study (Futreal et al., 1994). The evidence reported here supports a rather limited role of BRCA1 in breast carcinogenesis.

Adult↗
PubMed1985

Partial suppression of an ochre mutation in Saccharomyces cerevisiae by multicopy plasmids containing a normal yeast tRNAGln gene.

We screened a yeast genomic library for recombinant DNA plasmids that complemented the ultraviolet (u.v.) sensitivity of a strain of Saccharomyces cerevisiae designated rad4-3 that is defective in excision repair of DNA. A multicopy plasmid (pNF4000) with a 9.4 X 10(3) base-pair yeast DNA insert partially complemented the u.v. sensitivity of rad4-3, but not of two other rad4 allelic mutants (rad4-2 and rad4-4), or of other u.v.-sensitive rad mutants. The yeast insert was analyzed by restriction mapping, DNA-DNA hybridization, DNA-tRNA hybridization and DNA sequencing. This analysis revealed the presence of a normal tRNAGln gene, a yeast sigma element situated 5' to the transfer RNA gene, a Ty element and a solo delta element. Deletion analysis of pNF4000 showed that the tRNAGln gene is required for partial complementation of the u.v. sensitivity of rad4-3. Furthermore, a multicopy plasmid containing a tRNAGln gene derived from a different region of the yeast genome also partially complemented the u.v. sensitivity of rad4-3. The rad4-3 mutation is suppressed following transformation with a plasmid containing the known ochre suppressor SUP11-o, indicating that it is an ochre mutation. We therefore conclude that when expressed in sufficient quantity, normal tRNAGln (which usually decodes the sense codon CAA) can weakly suppress the nonsense ochre codon UAA, and suggest that this represents an example of wobble occurring at the first rather than at the third position of the codon.

Base Sequence↗
PubMed2006

Identification of a novel mutation and a genetic polymorphism of EVER1 gene in two families with epidermodysplasia verruciformis.

BACKGROUND: Epidermodysplasia verruciformis (EV) is a rare autosomal recessive disease. The main clinical features include three kinds of lesions, high risk of skin cancer, and abnormal susceptibility to HPV 5 and 8. Recent studies have shown that mutations in EVER1 and EVER2 genes are responsible for the condition. OBJECTIVE: In the present study, we investigated the molecular basis of EV in two families with EV. METHODS: PCR and direct sequencing of the EVER1 and EVER2 genes were used to identify and confirm the mutations in our probands in the two families. Direct sequencing and SacI digestion were used to detect the polymorphism of exon 6. RESULTS: Sequencing of the EVER1 and EVER2 genes revealed a novel mutation and a genetic polymorphism. The novel mutation by inserting CATGT after nucleotide 916 in exon 9 resulted in a nonsense mutation and a premature termination codon. Direct sequencing and SacI digestion revealed genotype frequencies of C457T, 457T, and 457C alleles in 16 individuals of EV families were of 9, 3, and 4, which were 26, 0, and 24 in 50 unrelated normal controls, respectively. To our knowledge, the novel mutation and genetic polymorphism have not been described in literatures. CONCLUSIONS: The growing number of mutations in EV pedigrees supports the hypothesis that EVER1 and EVER2 are the molecular basis of EV.

Adult↗
PubMed2004

A mutation in a novel ATP-dependent Lon protease gene in a kindred with mild mental retardation.

BACKGROUND: Identifying the genetic factors that contribute to memory and learning is limited by the complexity of brain development and the lack of suitable human models for mild disorders of cognition. METHODS: Previously, a disease locus was mapped for a mild type of nonsyndromic mental retardation (IQ between 50 and 70) to a 4.2-MB interval on chromosome 3p25-pter in a large kindred. The genes and transcripts within the candidate region were systematically analyzed for mutations by single-strand polymorphism analysis and DNA sequencing. RESULTS: A nonsense mutation causing a premature stop codon in a novel gene (cereblon; CRBN) was identified that encodes for an ATP-dependent Lon protease. The predicted protein sequence is highly conserved across species, and it belongs to a family of proteins that selectively degrade short-lived polypeptides and regulate mitochondrial replication and transcription. One member of the Lon-containing protein family is regionally expressed in the human hippocampus, an important neuroanatomic region that is involved in long-term potentiation and learning. The mutation in the CRBN gene described interrupts an N-myristoylation site and eliminates a casein kinase II phosphorylation site at the C terminus. CONCLUSIONS: A gene on chromosome 3p that is associated with mild mental retardation in a large kindred is reported. This finding implicates a role for the ATP-dependent degradation of proteins in memory and learning.

Adaptor Proteins, Signal Transducing↗
PubMed2000

A novel nonsense mutation (Q509X) in three Italian late-infantile neuronal ceroid-lipofuscinosis children.

We identified a novel nonsense CLN2 mutation (Q509X) in three Italian children with classical late-infantile neuronal ceroid lipofuscinosis (LINCL) from two unrelated families. The mutation introduced a premature stop codon in exon 12 of the CLN2 gene, resulting in a protein lacking the last 54 residues. Haplotype analysis suggested independent origin of the mutation in our families. The protein truncation test was employed to verify the functional consequences of the novel Q509X mutation. In Patient 1, the mutant alleles were transcribed but translated in a shorted peptide suggesting that the Q509X mutation is likely to interfere with CLN2p function. While expanding the list of genetic variants in LINCL, our findings represent the first molecular characterization of LINCL patients in South Europe.

Aminopeptidases↗
PubMed2001

Novel molecular defects in the androgen receptor gene of Mexican patients with androgen insensitivity.

The androgen insensitivity syndrome (AIS) is an X-linked form of male pseudohermaphroditism caused by mutations in the androgen receptor (AR) gene. In the present study, we analyzed the AR gene in 8 patients, 4 sporadic and 2 familial cases with the syndrome, using exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis and identified six new single base mutations, including one nonsense mutation at the hinge region of the receptor. These molecular lesions occurred in the steroid-binding domain (SBD) and all but one affected the first nucleotide of their respective codons. A nonsense mutation in exon 4, which converts a glutamine into a premature termination signal (Q657stop), a missense mutation changing arginine instead of glycine (G743R) and a conservative substitution of leucine with valine at amino acid 830 (L830V) were detected in patients with CAIS. Three other missense mutations located in exons 4 (L701I), 5 (A765S), and 6 (Q802R) were present in individuals bearing a partial form of AIS. These data allow us to reaffirm the view that nonsense mutations in the AR results almost invariably in a CAIS phenotype and underly the importance of the SBD for the AR functional activity.

Adult↗
PubMed2003

Viable nonsense mutants for the essential gene SUP45 of Saccharomyces cerevisiae.

BACKGROUND: Termination of protein synthesis in eukaryotes involves at least two polypeptide release factors (eRFs) - eRF1 and eRF3. The highly conserved translation termination factor eRF1 in Saccharomyces cerevisiae is encoded by the essential gene SUP45. RESULTS: We have isolated five sup45-n (n from nonsense) mutations that cause nonsense substitutions in the following amino acid positions of eRF1: Y53 --> UAA, E266 --> UAA, L283 --> UAA, L317 --> UGA, E385 --> UAA. We found that full-length eRF1 protein is present in all mutants, although in decreased amounts. All mutations are situated in a weak termination context. All these sup45-n mutations are viable in different genetic backgrounds, however their viability increases after growth in the absence of wild-type allele. Any of sup45-n mutations result in temperature sensitivity (37 degrees C). Most of the sup45-n mutations lead to decreased spore viability and spores bearing sup45-n mutations are characterized by limited budding after germination leading to formation of microcolonies of 4-20 cells. CONCLUSIONS: Nonsense mutations in the essential gene SUP45 can be isolated in the absence of tRNA nonsense suppressors.

Alleles↗