Relocalisation of β-globin coding sequences by myosin heavy chain and vimentin 3' untranslated regions
The presence of a localisation signal within the 3' untranslated regions of myosin heavy chain and vimentin messenger RNAs was investigated by studying mRNA distribution in myoblasts and fibroblasts which were transfected with β-globin and chimaeric β-globin-myosin and β-globin-vimentin gene constructs. In cells transfected with constructs containing either a fragment of the β-globin gene containing both coding and 3' untranslated sequences or the β-globin coding sequences alone, in situ hybridisation revealed that the mRNAs transcribed from these constructs were distributed throughout the cytoplasm without any evident localisation. In contrast, within cells transfected with constructs containing β-globin coding sequences linked to the myosin heavy chain or vimentin 3' untranslated sequences there was a strong perinuclear localisation of the chimaeric mRNAs. This indicated that loss of its 3' untranslated region does not affect distribution of β-globin mRNA whereas the 3' untranslated sequences of both myosin heavy chain and vimentin cause a relocalisation of β-globin mRNA. The ability of the myosin heavy chain 3' untranslated region to relocalise β-globin coding sequences was investigated in the more complex cellular environment of skeletal muscle by intra-muscular injection of β-globin and chimaeric β-globin-myosin constructs. In muscle injected with β-globin constructs in situ hybridisation revealed that mRNAs transcribed from these constructs were distributed throughout the muscle section with no apparent localisation.