Naturally occurring splicing variants of the hMSH2 gene containing nonsense codons identify possible mRNA instability motifs within the gene coding region.
We have identified certain unusually spliced cDNA species following PCR amplification of peripheral blood lymphocyte (PBL) mRNA from the hMSH2 gene. A naturally occurring transcript containing a nonsense codon due to the skipping of 5 exons was amplified from PBLs of several healthy individuals. A feature of this and another unusual splicing product was the presence of sequence motifs which bore significant similarity to mRNA instability determinants in the region immediately downstream of the stop codon. In particular, the rare tetranucleotide GAUG, previously identified in yeast as being of critical importance to the rapid degradation of nonsense-containing mRNAs was situated 23 base pairs downstream of the stop codon. Furthermore the region downstream of the stop codon was A:U rich and contained 2 copies of the AUUUA motif. As other forms of alternative splicing would not result in the same juxtaposition of stop codons and instability motifs, we suggest that the stop codons may have been deliberately introduced by the splicing process for their proximity to these destabilising motifs, and that splicing may play a role in channeling mRNAs into degradative pathways. These results are consistent with the hypothesis that nuclear factors may scan pre-mRNAs prior to splicing.
Marshall
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Departamento de Genética Humana, Instituto Nacional de Saúde, Lisboa, Portugal. p.loureir@pen.gulbenkian.pt
Isidro
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Boavida
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D000251:Adenosine Triphosphatases; D017398:Alternative Splicing; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D018389:Codon, Nonsense; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D014644:Genetic Variation; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D051719:MutS DNA Mismatch-Binding Protein; D051718:MutS Homolog 2 Protein; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
D001426:Bacterial Proteins; D018389:Codon, Nonsense; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D000251:Adenosine Triphosphatases; C497172:MSH2 protein, human; D051719:MutS DNA Mismatch-Binding Protein; D051718:MutS Homolog 2 Protein; C497175:MutS protein, E coli