Localization signals in the 3'untranslated region (3'UTR) of myosin heavy chain mRNA were investigated using hybrid gene constructs. In myoblasts transfected with constructs containing either both coding sequences and 3'UTR of the rabbit beta-globin gene or the beta-globin coding sequences alone in situ hybridization showed that globin transcripts were distributed throughout the cytoplasm with no localization. In contrast, in myoblasts transfected with beta-globin coding sequences linked to the myosin heavy chain 3'UTR there was strong perinuclear localization of the hybrid mRNA; this was maintained in myotubes. We conclude that myosin heavy chain 3'UTR contains a localization signal. (C) 1997 Academic Press Limited.