Quantification analysis of 5'-splice signal sequences in mRNA precursors. Mutations in 5'-splice signal sequence of human β-globin gene and β-thalassemia

Concerning the signals which direct excision of introns from mRNA precursors in higher eukaryotic genes, consensus 9-nucleotide sequence, ( C A ) AG/GT ( A G ) AGT , has been proposed with the 5′-splice site, but actual 5′-splice site sequences differ from it in a greater or lesser degree. We analyzed 5′-splice site sequence of human β -globin gene by quantification method (categorical discriminant analysis) proposed previously. Analyses of 13-nucleotide sequences and deleted sequences showed that 9-nucleotide sequences in the consensus region are almost sufficient to define 5′-splice signal. To confirm this view, we examined a number of β -globin mutant genes, where nucleotide changes occur at the authentic 5′-splice site of the first intron and cause β -thalassemia phenotype. Our method could explain why such mutations abolish the 5′-splice site and cryptic 5′-splice sites are activated.