A LOCALIZATION SIGNAL IN THE 3'-UNTRANSLATED REGION OF C-MYC MESSENGER-RNA TARGETS C-MYC MESSENGER-RNA AND BETA-GLOBIN REPORTER SEQUENCES TO THE PERINUCLEAR CYTOPLASM AND CYTOSKELETAL-BOUND POLYSOMES

There is increasing evidence that in mammalian cells some mRNAs are lo calised to specific parts of the cytoplasm and a proportion of mRNAs a nd polyribosomes are associated with the cytoskeleton, It has been sho wn previously that c-myc mRNA is present in the perinuclear cytoplasm and associated with the cytoskeleton, and that this localisation is de pendent upon the 3' untranslated region of the mRNA. The present studi es show that in transfected fibroblasts the c-myc 3' untranslated regi on is able to localise beta-globin reporter sequences to the perinucle ar cytoplasm. Studies with constructs containing deletions within the 3' untranslated region identify the region between bases 194 and 280 a s critical for localisation. Transfection of cells with constructs in which this region is linked to beta-globin sequences showed that it wa s sufficient to localise the chimaeric transcripts to the perinuclear cytoplasm and to cytoskeletal-bound polyribosomes. Transfection with c onstructs containing a mutated AUUUA sequence within the 194-280 base region showed that this conserved AUUUA is required for targeting of b oth c-myc mRNA and a chimaeric transcript of beta-globin transcripts l inked to the c-myc 3' untranslated region, The region between bases 19 4 and 280 did not induce instability of beta-globin transcripts and th e AUUUA mutation had little effect upon mRNA stability. We propose tha t this 86 nt region of the 3' untranslated region contains a localisat ion signal to target c-myc mRNA so that it is retained on cytoskeletal -bound polysomes in the perinuclear cytoplasm; a conserved AUUUA seque nce appears to be a critical part of this signal.