Two mutations in the beta-globin polyadenylylation signal reveal extended transcripts and new RNA polyadenylylation sites.

Abstract

Two mutations in the (-globin poly(A) signal were identified in Israeli patients with 3+-tasmia by sequence analysis following PCR. One is a point mutation (AATAAA AATAAG) and the other is a 5-base-par deletion (AATAAA A ). The mutant genes were used to investigate the function of the poly(A) signal in vivo and to evaluate the mechanism whereby these mutations lead to a thalassemic phenotype. Analysis of RNA derived from peripheral blood demonstrated the presence ofelongated RNA species in patients carrying either mutation. Other aspects of RNA processing (initiation, splicing) were unimpaired. RNA obtained from the patients carrying the point mutation contained four discrete, extended RNA species, 1500-2900 nucleotides long, which were found to be polyadenylylated. Some normal cleavagepolyadenylylation was also observed. The 5-base-pair deletion completely abolished cleavage at the normal site. This deletion mutation resulted in a phenotype of (3+-thaassemia, thus providing evidence that the extended mRNAs are translatable in vivo. Furthermore, additional transcripts, >5 kilobases, presumably mRNA precursors, were found in all RNA samples, induding those of nonthalassemic controls. The extended transcripts of the poly(A) mutants, together with the high molecular weight precursors, suggest that the human -globin gene transcription unit is significantly longer than previously recognized.

The Role of Nuclear Cap Binding Protein Cbc1p of Yeast in mRNA Termination and Degradation

“…The reduction in mRNA level caused by a mutation or deletion of the poly(A) signals has also been observed in the r293 mutation of the unc-54 gene in Caenorhabditis elegans, which involves deletion of the poly(A) signal in the myosin heavy chain B mRNA (58), and in human thalassemias resulting from mutations in the conserved AAUAAA polyadenylation signal (26,52,64). In C. elegans, several smg mutations were shown to suppress the unc-54 (r293) mutation, resulting in near-normal amounts of the unc-54 (r293) mRNA (8,58).…”

The Molecular Basis of -Thalassemia

“…Mutations affecting other sites in the 3 0 UTR, a C ! G substitution at nucleotide 6, and a 13 bp deletion at nucleotides 90 downstream from the termination codon, also result in b þ -thalassemia (Rund et al 1992;Hamid and Akbari 2011).…”

Clinical Expression of a Rare β-Globin Gene Mutation Co-Inherited with Haemoglobin E-Disease

“…The mutations lead to ß + -thalassaemia and even the homozygous patient expressed a mild form of ß-thalassaemia. Rund et al have shown in three patients in which the mutated AATAAG allele was the only gene capable of producing RNA for ß-globin, an expression of 12-34% of normally cleaved and poly^· adenylated ß-globin mRNA (15). This indicated that this particular type of mutation does not totally abolish cleavage and polyadenylation.…”

“…This indicated that this particular type of mutation does not totally abolish cleavage and polyadenylation. In addition, several studies have shown the existence of multiple elongated ß-globin mRNA's in patients carrying mutations in the poly(A) signal, indicating the use of alternative downstream AATAAA sites (15,16). It was suggested (16) and concluded (15) that part of these transcripts were translated, although inefficiently.…”