CM, Langston JW (1998a) Absence of mutations in the coding region of the alpha-synuclein gene in pathologically proven Parkinson's disease. Neurology 50:1136-1137 Chan P, Tanner CM, Jiang X, Langston JW (1998b) Failure to find the alpha-synuclein gene missense mutation (G209A) in 100 patients with younger onset Parkinson's disease. Neurology 50:513-514 Letters to the Editor

Summary. We have studied the expression of the silent b-thalassaemia term+6 (C fi G) mutation, at nucleotide 6 after the stop codon within the human b-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 b-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 b-globin mRNA. The term+6 mutation lies within a polypyrimidine track, similar to that in the b-intervening sequence II (b-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 b-globin gene may co-operate during b-globin mRNA biogenesis.

Locus control regions (LCRs)

SummaryThe mechanisms by which mutations within the 5¢ untranslated region (UTR) of the human b-globin gene (HBB) cause thalassaemia are currently not well understood. We present here the first comprehensive comparative functional analysis of four 'silent' mutations in the human b-globin 5¢UTR, namely: +10()T), +22(G fi A), +33(C fi G) and +(40-43)()AAAC), which are present in patients with b-thalassaemia intermedia. Expression of these genes under the control of the b-globin locus control region in stable transfected murine erythroleukaemia cells showed that all four mutations decreased steady state levels of mRNA to 61AE6%, 68%, 85AE2% and 70AE6%, respectively, compared with the wildtype gene. These mutations did not interfere with either mRNA transport from the nucleus to the cytoplasm, 3¢ end processing or mRNA stability. Nuclear run-on experiments demonstrated that mutations +10()T) and +33(C fi G) reduced the rate of transcription to a degree that fully accounted for the observed lower level of mRNA accumulation, suggesting a disruption of downstream promoter sequences. Interestingly, mutation +22(G fi A) decreased the rate of transcription to a low degree, indicating the existence of a mechanism that acts post-transcriptionally. Generally, our data demonstrated the significance of functionally analysing mutants of this type in the presence of a full complement of transcriptional regulatory elements within a stably integrated chromatin context in an erythroid cell environment.

No abstract