Posttranscriptional defects in beta-globin messenger RNA metabolism in beta-thalassemia: abnormal accumulation of beta-messenger RNA precursor sequences.
The production of beta-globin messenger RNA (mRNA) in beta-thalassemic erythroblasts was studied during pulse-chase incubations with [3H]uridine. Globin [3H]mRNA was quantitated by molecular hybridization to recombinant DNA probes complementary to globin mRNA and mRNA precursor sequences. Each of six patients with beta +-thalassemia produced normal amounts of globin alpha and beta [3H]mRNA during a 20-min pulse incubation, but the beta/alpha [3H]mRNA ratio declined to steady-state levels during a chase incubation, suggesting posttranscriptional defects in beta-globin mRNA metabolism. beta-globin mRNA precursor production was estimated by measurement of [3H]RNA sequences hybridizing to a pure DNA probe containing only the large intervening sequence (intron) of the beta-mRNA precursor. Four of the patients exhibited abnormal accumulation of 3H-beta-intron sequences (2-10 times normal), indicating abnormal posttranscriptional processing. In the remaining two patients, one of whom is known to carry a mutation in the small intron of the beta-globin gene, accumulation of large 3H beta-intron RNA and beta-globin [3H]mRNA was normal in nuclei, but the ratio of beta/alpha [3H]mRNA in cytoplasm was reduced, suggesting a different posttranscriptional defect in beta-mRNA processing. These findings imply the existence of heterogeneous posttranscriptional abnormalities in beta-globin mRNA metabolism in different patients with beta-thalassemia. The initial rates of gamma- and delta-mRNA synthesis were low in all patients, suggesting that the low level of expression of these genes in adults is mediated at the transcriptional level.
D000293:Adolescent; D000328:Adult; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002648:Child; D003593:Cytoplasm / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism / Q000648:ultrastructure; D005914:Globins / Q000235:genetics*; D006801:Humans; D009693:Nucleic Acid Hybridization; D009694:Nucleic Acid Precursors / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D013789:Thalassemia / Q000209:etiology / Q000235:genetics*; D014158:Transcription, Genetic
D009694:Nucleic Acid Precursors; D012333:RNA, Messenger; D005914:Globins