THE 3'-UNTRANSLATED REGION PLAYS A ROLE IN THE TARGETING OF METALLOTHIONEIN-I MESSENGER-RNA TO THE PERINUCLEAR CYTOPLASM AND CYTOSKELETAL-BOUND POLYSOMES

The mechanism of localisation of metallothionein-I (MT-I) mRNA was stu died in transfected cells by in situ hybridisation and cell fractionat ion. Hepatoma cells were transfected with the 5'-untranslated region a nd coding region of the beta-globin gene alone or linked to either the beta-globin 3'-untranslated region (3'-UTR) or the MT-I 3'-UTR. The w ild-type beta-globin mRNA and the beta-globin mRNA lacking its native 3'-UTR were present in free and cytoskeletal-bound polysomes to a simi lar extent and showed no localisation. Chimaeric globin-metallothionei n transcripts were significantly enriched in cytoskeletal-bound polyso mes and were localised in the perinuclear cytoplasm. Chimaeric globin- metallothionein and wild-type globin transcripts were of similar stabi lity. Chinese Hamster Ovary cells were transfected with constructs in which the MT-I 5'-untranslated region and coding sequences were linked to either the endogenous 3'-UTR or the glutathione peroxidase 3'-UTR. Wild-type MT-I transcripts were localised in the perinuclear cytoplas m but the chimaeric MT-I-glutathione peroxidase transcripts showed no distinct localisation. The results indicate that the 3'-UTR of MT-I mR NA contains a localisation signal which promotes both the association of the mRNA with the cytoskeleton and its perinuclear localisation. (C ) 1997 Elsevier Science B.V.