A nonsense mutation is responsible for the RNA-negative phenotype in human citrullinaemia.
Citrullinaemia is an inborn error of metabolism resulting from a deficiency of argininosuccinate synthetase. Previous studies of RNA of argininosuccinate synthetase of citrullinaemia patients using S1 nuclease analysis have identified a class of so-called RNA-negative alleles in which no stable mRNA can be detected. To investigate the nature of mutation responsible for such a phenotype, a compound heterozygous citrullinaemia carrying an RNA-negative allele and an allele with a 3' splice site mutation in intron 6 (IVS6-2A>G) was analysed. Using sequences of a DNA polymorphism and the IVS6-2A>G mutation as markers, approximately equal amounts of pre-mRNAs from allelic genes were detected suggesting that RNA-negative phenotype could not be the result of defect in transcription initiation. A C-to-T transition converting the CGA arginine codon at residue 279 to a TGA termination codon (R279X) was identified by cDNA sequencing. No accumulation of partially spliced pre-mRNAs containing introns immediately upstream and downstream of the nonsense mutation was observed. In addition, no mRNA species of abnormal size was detected when cDNA from the RNA-negative allele was analysed. Hence, there is no indication of nonsense-associated altered splicing (NAS). The most likely event responsible for the RNA-negative phenotype appears to be nonsense-mediated mRNA decay (NMD).
Li
C M
CM
Institute of Genetics, National Yang-Ming University, Taipei, Taiwan, Republic of China.
Chao
H K
HK
Liu
Y F
YF
Su
T S
TS
D000483:Alleles; D017398:Alternative Splicing / Q000235:genetics; D001124:Argininosuccinate Synthase / Q000235:genetics*; D020159:Citrullinemia / Q000201:enzymology / Q000235:genetics*; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D006801:Humans; D007438:Introns / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D018807:Polymorphism, Single-Stranded Conformational; D012313:RNA / Q000235:genetics* / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism
D018389:Codon, Nonsense; D018076:DNA, Complementary; D012322:RNA Precursors; D012313:RNA; D001124:Argininosuccinate Synthase