A 5' splice-region G----C mutation in exon 1 of the human beta-globin gene inhibits pre-mRNA splicing: a mechanism for beta+-thalassemia.
We have characterized a Mediterranean beta-thalassemia allele containing a sequence change at codon 30 that alters both beta-globin pre-mRNA splicing and the structure of the hemoglobin product. Presumably, this G----C transversion at position -1 of intron 1 reduces severely the utilization of the normal 5' splice site since the level of the Arg----Thr mutant hemoglobin (designated hemoglobin Kairouan) found in the erythrocytes of the patient is very low (2% of total hemoglobin). Since no natural mutations of the guanine located at position -1 of the CAG/GTAAGT consensus sequence had been isolated previously, we investigated the role of this nucleotide in the constitution of an active 5' splice site by studying the splicing of the pre-mRNA in cell-free extracts. We demonstrate that correct splicing of the mutant pre-mRNA is 98% inhibited. Our results provide further insights into the mechanisms of pre-mRNA maturation by revealing that the last residue of the exon plays a role at least equivalent to that of the intron residue at position +5.
Vidaud
M
M
Institut National de la Santé et de la Recherche Médicale U.91, Hôpital Henri Mondor, Creteil, France.
Gattoni
R
R
Stevenin
J
J
Vidaud
D
D
Amselem
S
S
Chibani
J
J
Rosa
J
J
Goossens
M
M
D000328:Adult; D001483:Base Sequence; D003001:Cloning, Molecular; D003596:Cytosine; D005091:Exons; D005260:Female; D005796:Genes; D005838:Genotype; D005914:Globins / Q000235:genetics*; D006147:Guanine; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D012322:RNA Precursors / Q000235:genetics*; D012326:RNA Splicing; D012016:Reference Values; D013789:Thalassemia / Q000097:blood / Q000235:genetics*
D012322:RNA Precursors; D006147:Guanine; D003596:Cytosine; D005914:Globins