scholarly journals Sequencing Analysis and Enzyme Activity Assay of SrUGT76G1 Revealed the Mechanism Toward on/off Production of Rebaudioside-A in Stevia Plants

2021 ◽  
Author(s):  
Simone Ribeiro Lucho ◽  
Marcelo do Amaral ◽  
Valmor Bianchi ◽  
Lorena Almagro ◽  
Maria Ferrer ◽  
...  
Keyword(s):  
Stop Codon ◽  
Premature Stop Codon ◽  
Binding Pocket ◽  
Structural Features ◽  
Steviol Glycosides ◽  
Sequencing Analysis ◽  
Structural Level ◽  
Rebaudioside A ◽  
Enzyme Activity Assay ◽  
Structure Activity

Abstract Stevia plants is known for its ability to synthesize steviol glycosides (SGs), a natural sweetener blend. Stevioside (STEV) and Rebaudioside-A (Reb-A) are the main SGs. However, Reb-A is more palatable than STEV and shows reduced bitter aftertaste. SrUGT76G1 catalyzes the conversion of STEV to Reb-A, improving their organoleptic properties. The better understanding of the structure/activity of SrUGT76G1 would allow shedding light up on on/off production of Reb-A in stevia plants. Thus, we analyzed the STEV and Reb-A content in stevia leaves of plants from Brazil and Spain and did not find detectable levels of Reb-A in Brazilian samples (off production). For this reason, we used a sequencing tool to study at the genetic and structural level the SrUGT76G1 gene. Changes in key amino acid residues in Brazilian samples were found, such as Leu204Phe, Thr284Leu and Leu126Ile. Leu204Phe mutants can narrow substrate-binding pocket to favor flavonoids recognition and decrease SGs synthesis, while Thr284 is considered key for 1,3-glucosylation of SGs, including Reb-A. These punctual mutations may partly explain the lack of functionality of UGT76G1 enzyme and off production of Reb-A in stevia plants from Brazil. Following this trend, Brazilian samples exhibited a T-to-A substitution, resulting in premature stop codon. As expected, the relative expression of SrUGT76G1 gene showed a higher level in Spanish samples than in Brazilian ones. Collectively, the results presented here show the structure-activity interplay of SrUGT76G1 enzyme and provide new insights on structural features and its role toward Reb-A synthesis.

scholarly journals Molecular structure of soybean E-genes and their functional mutations

2020 ◽  
pp. 3-13
Author(s):  
O. Okhrymovych ◽  
◽  
S. Chebotar ◽  
G. Chebotar ◽  
D. Zharikova ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Genetic Network ◽  
Structural Features ◽  
Loss Of Function ◽  
Nucleotide Substitutions ◽  
Early Maturity ◽  
E Gene ◽  
Wide Range

In this review, we discuss features of the molecular structure of known E-loci (early maturity) and their involvement in signaling to plant flowering, depending on the sensitivity of soybean genotypes to the photoperiod. These loci contribute to the adaptation of plants to a wide range of natural conditions due to mutations in genes and QTL that control flowering time. At the molecular level, E-genes are significantly different in structural features, origin and function. The lenghth of the identified genes range from one exon to 525 bp encoding the transcription factor (E1), up to 14 exons and about 20 kb for the GmGIa gene (E2). Among the functional mutations that in most cases lead to partial or complete loss of function, there are single-nucleotide substitutions or deletions, insertions of transposon-like sequences that can lead to amino acid substitutions in the protein, shift of the reading frame, appearance of the premature stop-codon. E-gene products are receptors of signals coming from the environment and they participate in signaling pathways that control the photoperiod. The overall impact and interactions between E-genes have not been fully studied yet, the molecular structure was investigated only for E1-E4, for which a genetic network of interactions was proposed, while at the same time five loci (E6-E9 and E11) were only mapped on soybean chromosomes, and the existence of a separate E5 locus has not yet been established. In eight of the 11 E-loci, the dominant allele causes late flowering. Also there is a pleiotropic effect of E-gene alleles on yield, plant height, stress resistance, and response to low temperatures. Knowledge of the allelic state of only some of the 11 genes is not sufficient. A comprehensive understanding of the functioning of the photoperiodic genetic response network is needed. E-genes are genetic determinants that can be used during selection and creation of new varieties with programmed rates of development.

scholarly journals First description of antimicrobial resistance in carbapenem-susceptible Klebsiella pneumoniae after imipenem treatment, driven by outer membrane remodeling

2020 ◽  
Author(s):  
Xuebin Tian ◽  
Qiongdan Wang ◽  
Laura Perlaza-Jiménez New ◽  
Xiangkuo Zheng ◽  
Yajie Zhao ◽  
...  
Keyword(s):  
Klebsiella Pneumoniae ◽  
Outer Membrane ◽  
Gel Electrophoresis ◽  
Stop Codon ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Premature Stop Codon ◽  
Sequencing Analysis ◽  
Membrane Remodeling ◽  
Carbapenem Resistant

Abstract Background:The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a looming threat to human health. Although there are numerous studies regarding porin alteration in association with the production of ESBLs and/or AmpC β-lactamase, a systematic study on the treatment-emergence of porins alteration in antibiotic resistance does not yet exist. The aim of this study was to investigate the underlying mechanism and evolution of resistance of K. pneumoniae during carbapenem treatment. Results:Here, we report three strains (FK-2624, FK-2723 and FK-2820) isolated from one patient before and after imipenem treatment during hospitalization. Antibiotic susceptibility testing indicated that that the first isolate, FK-2624, was susceptible to almost all tested antimicrobials, being resistant only to fosfomycin. The subsequent isolates FK-2723 and FK-2820 were multidrug resistant (MDR). After imipenem therapy, FK-2820 had evolved to be carbapenem-resistant. PCR and Genome Sequencing analysis indicated that oqxA, and fosA5, were identified in all three strains. In addition, FK-2624 also harbored bla SHV-187 and blaTEM-116. The blaSHV-187 and blaTEM-116 genes were not detected in FK-2723 and FK-2820. blaDHA-1, qnrB4, aac (6’)-IIc, and blaSHV-12, EreA2, CatA2, SulI, and tetD , were identified in both FK-2723 and FK-2820. Moreover, the genes bla DHA -1, qnrB4, aac(6’)-IIc were co-harbored on a plasmid. Of the virulence factors found in this study, ybtA, ICEKp6, mrkD, entB, iroN, rmpA2-6, wzi16 and capsular serotype K57 were found in the three isolates. The results of pairwise comparisons, multi-locus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) revealed high homology among the isolates. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that isolate FK-2820 lacked OmpK36, with genome sequence data validating that there was a premature stop codon in the ompK36 gene and real-time RT-PCR suggesting high turnover of the ompK36 non-sense transcript in FK-2820, with the steady-state mRNA level 0.007 relative to the initial isolate. Conclusion:This study in China highlight that the alteration of outer membrane porins due to the 14-day use of imipenem play a potential role in leading to clinical presentation of carbapenem-resistance. This is the first description of increased resistance developing from a carbapenem-susceptible K. pneumoniae with imipenem treatment driven by outer membrane remodeling.

Identification of New CD177 Isoform in NB1 Deficient Individuals

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1270-1270
Author(s):  
Behnaz Bayat ◽  
Karin Kissel ◽  
Silke Werth ◽  
Sentot Santoso
Keyword(s):  
Stop Codon ◽  
High Surface ◽  
Specific Antigen ◽  
Premature Stop Codon ◽  
Transcriptional Analysis ◽  
Sequencing Analysis ◽  
Short Transcript ◽  
Rabbit Polyclonal Antibody ◽  
Protein Isoform

Abstract Human neutrophil-specific antigen CD177 (NB1; HNA-2a) belongs to the member of the cyctein-rich LY-6 superfamily. Transcriptional analysis of this family revealed intron-retaining mechanism, which produce many spliced forms of gene. In some cases, this mis-spliced isoform was the most abundant form suggesting a control mechanism of gene expression. CD177 glycoprotein carries neutrophil antigen HNA-2a, and antibodies to HNA-2a frequently causes transfusion related acute lung injury (TRALI). Recently, CD177 has been found to be associated with the expression of proteinase-3 (PR3) which plays a role in autoantibody mediated Wegener’s granulomatosis. Neutrophils from some people lack CD177 (termed HNA-2a negative), however, the mechanism responsible for this deficiency is not fully understood. In this study, we investigated whether mis-spliced form of CD177 exist in neutrophils. Neutrophil from blood donors were phenotyped for the presence or absence of CD177 by flow cytometry using two mabs 7D8, MEM166 recognising different epitopes on CD177. HNA-2a positive individuals carrying high surface CD177 density and HNA-2a negative individuals were selected. mRNA was isolated from CD177 phenotyped individuals and were analyzed by PCR using different sets of primer set. Amplification of CD177 transcript (bases 98–1401) showed the expected ~1300 bp band encoding for the entire CD177 (isoform 1), and a smaller band (~417bp) with similar intensity in HNA-2a positive as well as in HNA-2a negative individuals. Sequencing analysis of the short transcript showed the presence of intronic sequence between exon 3 and 4, which produces premature stop codon. Transfection of insect cells with related transcript resulted in production of a ~23 kDa protein which is detectable in immunoblot using rabbit polyclonal antibody against synthetic CD177 peptide. This ~23 kDa protein (isoform 4) did not react with mabs 7D8 and MEM166. Furthermore, immunoblotting analysis of other blood cells showed that isoform 4 was exclusively found on neutrophils. In contrast to the isoform 1, isoform 4 was not upregulated on neutrophils of individuals receiving GCSF. Neutrophils treated with fMLP in vitro showed down-regulation of isoform 4 transcript. This phenomenon however, has not been observed in neutrophils treated with LPS and IL-8. In summary, we characterized a new CD177 isoform in neutrophils. The presence of this isoform in both HNA-2a positive and negative CD177 phenotyped individuals and its regulation with fMLP indicate the role of this protein in inflammatory process.

scholarly journals Aberrant Splicing of SDHC in Families With Unexplained Succinate Dehydrogenase-Deficient Paragangliomas

2020 ◽  
Vol 4 (12) ◽  
Author(s):  
Sunita M C De Sousa ◽  
John Toubia ◽  
Tristan S E Hardy ◽  
Jinghua Feng ◽  
Paul Wang ◽  
...  
Keyword(s):  
Succinate Dehydrogenase ◽  
Transcriptome Analysis ◽  
Haplotype Analysis ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Chromosome 1 ◽  
Sequencing Analysis ◽  
Kit Mutation ◽  
Whole Exome ◽  
Genetic Test Results

Abstract Context Germline mutations in the succinate dehydrogenase genes (SDHA/B/C/D, SDHAF2—collectively, “SDHx”) have been implicated in paraganglioma (PGL), renal cell carcinoma (RCC), gastrointestinal stromal tumor (GIST), and pituitary adenoma (PA). Negative SDHB tumor staining is indicative of SDH-deficient tumors, usually reflecting an underlying germline SDHx mutation. However, approximately 20% of individuals with SDH-deficient tumors lack an identifiable germline SDHx mutation. Methods We performed whole-exome sequencing (WES) of germline and tumor DNA followed by Sanger sequencing validation, transcriptome analysis, metabolomic studies, and haplotype analysis in 2 Italian-Australian families with SDH-deficient PGLs and various neoplasms, including RCC, GIST, and PA. Results Germline WES revealed a novel SDHC intronic variant, which had been missed during previous routine testing, in 4 affected siblings of the index family. Transcriptome analysis demonstrated aberrant SDHC splicing, with the retained intronic segment introducing a premature stop codon. WES of available tumors in this family showed chromosome 1 deletion with loss of wild-type SDHC in a PGL and a somatic gain-of-function KIT mutation in a GIST. The SDHC intronic variant identified was subsequently detected in the second family, with haplotype analysis indicating a founder effect. Conclusions This is the deepest intronic variant to be reported among the SDHx genes. Intronic variants beyond the limits of standard gene sequencing analysis should be considered in patients with SDH-deficient tumors but negative genetic test results.

scholarly journals A Novel Mutation in theCYP11B1Gene Causes Steroid 11β-Hydroxylase Deficient Congenital Adrenal Hyperplasia with Reversible Cardiomyopathy

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Mohammad A. Alqahtani ◽  
Ayed A. Shati ◽  
Minjing Zou ◽  
Ali M. Alsuheel ◽  
Abdullah A. Alhayani ◽  
...  
Keyword(s):  
Congenital Adrenal Hyperplasia ◽  
Stop Codon ◽  
Novel Mutation ◽  
Skin Pigmentation ◽  
Premature Stop Codon ◽  
Molecular Defect ◽  
Sequencing Analysis ◽  
Adrenal Hyperplasia ◽  
Biallelic Mutation ◽  
Hydroxylase Deficiency

Congenital adrenal hyperplasia (CAH) due to steroid 11β-hydroxylase deficiency is the second most common form of CAH, resulting from a mutation in theCYP11B1gene. Steroid 11β-hydroxylase deficiency results in excessive mineralcorticoids and androgen production leading to hypertension, precocious puberty with acne, enlarged penis, and hyperpigmentation of scrotum of genetically male infants. In the present study, we reported 3 male cases from a Saudi family who presented with penile enlargement, progressive darkness of skin, hypertension, and cardiomyopathy. The elder patient died due to heart failure and his younger brothers were treated with hydrocortisone and antihypertensive medications. Six months following treatment, cardiomyopathy disappeared with normal blood pressure and improvement in the skin pigmentation. The underlying molecular defect was investigated by PCR-sequencing analysis of all coding exons and intron-exon boundary of theCYP11B1gene. A novel biallelic mutation c.780 G>A in exon 4 of theCYP11B1gene was found in the patients. The mutation created a premature stop codon at amino acid 260 (p.W260∗), resulting in a truncated protein devoid of 11β-hydroxylase activity. Interestingly, a somatic mutation at the same codon (c.779 G>A,p.W260∗) was reported in a patient with papillary thyroid cancer (COSMIC database). In conclusion, we have identified a novel nonsense mutation in theCYP11B1gene that causes classic steroid 11β-hydroxylase deficient CAH. Cardiomyopathy and cardiac failure can be reversed by early diagnosis and treatment.

A New Germline Stop Codon Mutation in Exon 15 of the APC Gene Predisposing to Familial Adenomatous Polyposis

2013 ◽  
Vol 28 (4) ◽  
pp. 405-408 ◽  
Author(s):  
Laura Schirosi ◽  
Marcello Pellegrino ◽  
Paolo Tarantino ◽  
Salvatore Mauro ◽  
Andrea Tinelli ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Familial Adenomatous Polyposis ◽  
Germline Mutation ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Colorectal Tumor ◽  
Apc Gene ◽  
Sequencing Analysis ◽  
Adenomatous Polyposis ◽  
Truncated Protein

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder related to germline mutations of the adenomatous polyposis coli ( APC) gene. It is characterized by the detection of numerous adenomatous polyps that, if untreated, develop into colorectal cancer. We studied an Italian family with FAP history and the related colorectal tumor sample of the proband. Sequencing analysis of blood samples revealed the presence of a never-reported germline mutation in the APC gene (exon 15): an heterozygous G deletion at position c.2126 resulting in a premature stop codon (p.Gly721GlufsX6) and in a truncated protein. This mutation was also identified in the colorectal tumor tissue, together with a second known pathogenic heterozygotic somatic mutation, c.4348C>T (p.Arg1450X), which generates a premature truncated protein. The novel identified germline mutation is therefore related to FAP and, in accordance with Knudson's “two hit” hypothesis, can be considered the first event predisposing to the insurgence of colorectal cancer in these patients. The somatic hit inactivating the second allele of the APC gene is located in the mutation cluster region of the gene; this is not a random event since it depends on the position of the germline mutation. The inactivation of APC generates the neoplastic growth advantage to the cell.

scholarly journals First description of antimicrobial resistance in carbapenem-susceptible Klebsiella pneumoniae after imipenem treatment, driven by outer membrane remodeling.

2020 ◽  
Author(s):  
Xuebin Tian ◽  
Qiongdan Wang ◽  
Laura Perlaza-Jiménez ◽  
Xiangkuo Zheng ◽  
Yajie Zhao ◽  
...  
Keyword(s):  
Klebsiella Pneumoniae ◽  
Outer Membrane ◽  
Gel Electrophoresis ◽  
Stop Codon ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Premature Stop Codon ◽  
Sequencing Analysis ◽  
Membrane Remodeling ◽  
Carbapenem Resistant

Abstract Background: The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a looming threat to human health. Although there are numerous studies regarding porin alteration in association with the production of ESBLs and/or AmpC β-lactamase, a systematic study on the treatment-emergence of porins alteration in antibiotic resistance does not yet exist. The aim of this study was to investigate the underlying mechanism of resistance of K. pneumoniae during carbapenem treatment. Results: Here, we report three strains (FK-2624, FK-2723 and FK-2820) isolated from one patient before and after imipenem treatment during hospitalization. Antibiotic susceptibility testing indicated that that the first isolate, FK-2624, was susceptible to almost all tested antimicrobials, being resistant only to fosfomycin. The subsequent isolates FK-2723 and FK-2820 were multidrug resistant (MDR). After imipenem therapy, FK-2820 was found to be carbapenem-resistant. PCR and Genome Sequencing analysis indicated that oqxA, and fosA5, were identified in all three strains. In addition, FK-2624 also harbored blaSHV-187 and blaTEM-116. The blaSHV-187 and blaTEM-116 genes were not detected in FK-2723 and FK-2820. blaDHA-1, qnrB4, aac (6’)-IIc, and blaSHV-12, EreA2, CatA2, SulI, and tetD, were identified in both FK-2723 and FK-2820. Moreover, the genes blaDHA-1, qnrB4, aac (6’)-IIc were co-harbored on a plasmid. Of the virulence factors found in this study, ybtA, ICEKp6, mrkD, entB, iroN, rmpA2-6, wzi16 and capsular serotype K57 were found in the three isolates. The results of pairwise comparisons, multi-locus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) revealed high homology among the isolates. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that isolate FK-2820 lacked OmpK36, with genome sequence data validating that there was a premature stop codon in the ompK36 gene and real-time RT-PCR suggesting high turnover of the ompK36 non-sense transcript in FK-2820, with the steady-state mRNA level 0.007 relative to the initial isolate. Conclusion: This study in China highlight that the alteration of outer membrane porins due to the 14-day use of imipenem play a potential role in leading to clinical presentation of carbapenem-resistance. This is the first description of increased resistance developing from a carbapenem-susceptible K. pneumoniae with imipenem treatment driven by outer membrane remodeling.

scholarly journals Low Frequency of Ceftazidime-Avibactam Resistance among Enterobacteriaceae Isolates Carrying blaKPC Collected in U.S. Hospitals from 2012 to 2015

2016 ◽  
Vol 61 (3) ◽  
Author(s):  
Mariana Castanheira ◽  
Rodrigo E. Mendes ◽  
Helio S. Sader
Keyword(s):  
Efflux Pump ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Low Frequency ◽  
Resistance Mechanisms ◽  
Sequencing Analysis ◽  
Relative Quantification ◽  
Large Collection ◽  
Icu Patients ◽  
Content Type

ABSTRACT Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae isolates have been increasingly reported worldwide, and therapeutic options to treat infections caused by these organisms are limited. We evaluated the activity of ceftazidime-avibactam and comparators against 456 Enterobacteriaceae isolates carrying bla KPC collected from 79 U.S. hospitals during 2012 to 2015. Overall, ceftazidime-avibactam (MIC50/90, 0.5/2 μg/ml; 99.3% susceptible) and tigecycline (MIC50/90, 0.5/1 μg/ml; 98.9% susceptible at ≤2 μg/ml) were the most active agents. Only 80.5% and 59.0% of isolates were susceptible to colistin and amikacin, respectively. All three isolates (0.7%) displaying resistance to ceftazidime-avibactam (K. pneumoniae; MICs, ≥16 μg/ml) were evaluated using whole-genome sequencing analysis and relative quantification of expression levels of porins and efflux pump. Two isolates carried metallo-β-lactamase genes, bla NDM-1 or bla VIM-4, among other β-lactam resistance mechanisms, and one displayed a premature stop codon in ompK35 and decreased expression of ompK36. Ceftazidime-avibactam was active against 100.0 and 99.3% of isolates carrying bla KPC-3 (n = 221) and bla KPC-2 (n = 145), respectively. Isolates carrying bla KPC were more commonly recovered from pneumonia (n = 155), urinary tract (n = 93), and skin/soft tissue (n = 74) infections. Ceftazidime-avibactam (97.8 to 100.0% susceptible) was consistently active against isolates from all infection sites. K. pneumoniae (83.3% of the collection) susceptibility rates were 99.2% for ceftazidime-avibactam, 98.9% for tigecycline, and 80.1% for colistin. Ceftazidime-avibactam susceptibility did not vary substantially when comparing isolates from intensive care unit (ICU) patients to those from non-ICU patients. Ceftazidime-avibactam was active against this large collection of isolates carrying bla KPC and represents a valuable addition to the armamentarium currently available for the treatment of infections caused by KPC-producing Enterobacteriaceae.

HAZARD: An Expert System for Risk Assessment of Environmental Chemicals

1987 ◽  
Vol 26 (01) ◽  
pp. 13-23 ◽  
Author(s):  
H. W. Gottinger
Keyword(s):  
Expert System ◽  
Structural Information ◽  
Chemical Carcinogenesis ◽  
Structural Features ◽  
Environmental Chemicals ◽  
Chemical Carcinogens ◽  
Carcinogenic Activity ◽  
Current State ◽  
Structure Activity ◽  
Carcinogenic Potential

AbstractThe purpose of this paper is to report on an expert system in design that screens for potential hazards from environmental chemicals on the basis of structure-activity relationships in the study of chemical carcinogenesis, particularly with respect to analyzing the current state of known structural information about chemical carcinogens and predicting the possible carcinogenicity of untested chemicals. The structure-activity tree serves as an index of known chemical structure features associated with carcinogenic activity. The basic units of the tree are the principal recognized classes of chemical carcinogens that are subdivided into subclasses known as nodes according to specific structural features that may reflect differences in carcinogenic potential among chemicals in the class. An analysis of a computerized data base of known carcinogens (knowledge base) is proposed using the structure-activity tree in order to test the validity of the tree as a classification scheme (inference engine).

Ectopic Transcript Analysis Indicates that Allelic Exclusion is an Important Cause of Type I Protein C Deficiency in Patients with Nonsense and Frameshift Mutations in the PROC Gene

1996 ◽  
Vol 75 (06) ◽  
pp. 870-876 ◽  
Author(s):  
José Manuel Soria ◽  
Lutz-Peter Berg ◽  
Jordi Fontcuberta ◽  
Vijay V Kakkar ◽  
Xavier Estivill ◽  
...  
Keyword(s):  
Splice Site ◽  
Protein C ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Allelic Exclusion ◽  
Polymorphism Analysis ◽  
Type I ◽  
Protein C Deficiency ◽  
Nonsense Mutations ◽  
Stop Codons

SummaryNonsense mutations, deletions and splice site mutations are a common cause of type I protein C deficiency. Either directly or indirectly by altering the reading frame, these' lesions generate or may generate premature stop codons and could therefore be expected to result in premature termination of translation. In this study, the possibility that such mutations could instead exert their pathological effects at an earlier stage in the expression pathway, through “allelic exclusion” at the RNA level, was investigated. Protein C (PROC) mRNA was analysed in seven Spanish type I protein C deficient patients heterozygous for two nonsense mutations, a 7bp deletion, a 2bp insertion and three splice site mutations. Ectopic RNA transcripts from patient and control lymphocytes were analysed by RT-PCR and direct sequencing of amplified PROC cDNA fragments. The nonsense mutations and the deletion were absent from the cDNAs indicating that only mRNA derived from the normal allele had been expressed. Similarly for the splice site mutations, only normal PROC cDNAs were obtained. In one case, exclusion of the mutated allele could be confirmed by polymorphism analysis. In contrast to these six mutations, the 2 bp insertion was not associated with loss of mRNA from the mutated allele. In this case, cDNA analysis revealed the absence of 19 bases from the PROC mRNA consistent with the generation and utilization of a cryptic splice site 3’ to the site of mutation, which would result in a frameshift and a premature stop codon. It is concluded that allelic exclusion is a common causative mechanism in those cases of type I protein C deficiency which result from mutations that introduce premature stop codons

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