The beta-globin C-->G mutation at 6 bp 3' to the termination codon causes beta-thalassaemia by decreasing the mRNA level.
We have studied the expression of the silent beta-thalassaemia term+6 (C-->G) mutation, at nucleotide 6 after the stop codon within the human beta-globin 3' untranslated regions (3'UTR), by stable transfection in murine erythroleukaemia (MEL) cells. Steady state mRNA levels from transfected MEL cells containing the term+6 mutant allele were reduced by 52-60%, compared with those obtained from the normal beta-globin gene, in both total and cytoplasmic RNA fractions, showing that the mutation itself is responsible for the similar data obtained from patients. Upon analysis of nuclear RNA, the term+6 mutation was found to also lower the ratio of cleaved/uncleaved transcripts by 22-30%, thus revealing that it interferes with correct 3'-end formation of beta-globin mRNA. The term+6 mutation lies within a polypyrimidine track, similar to that in the beta-intervening sequence II (beta-IVSII), which is known to be an important contributor to the promotion of premRNA 3'-end formation. We propose that the two polypyrimidine tracks flanking the translated region of exon III of the human beta-globin gene may co-operate during beta-globin mRNA biogenesis.
Sgourou
Argyro
A
Laboratory of Biology, Faculty of Medicine, University of Patras, Patras, Rion, 261-10 Greece.
Papachatzopoulou
Adamandia
A
Psiouri
Lambrini
L
Antoniou
Michael
M
Zoumbos
Nicholas
N
Gibbs
Richard
R
Athanassiadou
Aglaia
A
D002648:Child; D018388:Codon, Terminator; D005914:Globins / Q000235:genetics*; D006801:Humans; D008297:Male; D009154:Mutation / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection; D017086:beta-Thalassemia / Q000235:genetics*
D018388:Codon, Terminator; D012333:RNA, Messenger; D005914:Globins