The enterovirus 5 nontranslated region (NTR) contains an internal ribosome entry site (IRES), which facilitates translation initiation of the viral open reading frame in a 5 (m 7 GpppN) cap-independent manner, and cis-acting signals for positive-strand RNA replication. For several enteroviruses, the 5 NTR has been shown to determine the virulence phenotype. We have constructed a chimera consisting of the putative IRES element from the Travis strain of echovirus 12 (ECV12), a wild-type, relatively nonvirulent human enterovirus, exchanged with the homologous region of a full-length infectious clone of coxsackievirus B3 (CBV3). The resulting chimera, known as ECV12(5NTR)CBV3, replicates similarly to CBV3 in human and simian cell lines yet, unlike CBV3, is completely restricted for growth on two primary murine cell lines at 37°C. By utilizing a reverse-genetics approach, the growth restriction phenotype was localized to the predicted stem-loop II within the IRES of ECV12. In addition, a revertant of ECV12(5NTR)CBV3 was isolated which possessed three transition mutations and had restored capability for replication in the utilized murine cell lines. Assays for cardiovirulence indicated that the ECV12 IRES is responsible for a noncardiovirulent phenotype in a murine model for acute myocarditis. The results indicate that the 5 NTRs of ECV12 and CBV3 exhibit variable intracellular requirements for function and serve as secondary determinants of tissue or species tropism.The Enterovirus genus within the family Picornaviridae contains human pathogens responsible for clinical syndromes involving multiple tissues and organ systems (reviewed in reference 37). The enteroviruses, like all members of the family Picornaviridae, are positive-stranded, nonenveloped RNA viruses which possess a characteristic icosahedral capsid. This genus is subdivided into five groups: the polioviruses, coxsackievirus groups A and B, echoviruses, and the numbered enteroviruses. The ϳ7.4-kb enterovirus genome is structurally similar to eukaryotic mRNA in several respects: a single open reading frame encoding structural and nonstructural proteins is flanked by 5Ј and 3Ј nontranslated regions (NTRs) and a 3Ј polyadenylated tail. The 5Ј NTR is highly structured, containing six predicted secondary structural domains, or stem-loops (SLs) (44, 52), and carries out functions crucial to the life cycle of the virus (2, 42). In addition, the 5Ј NTR has been shown to influence the virulence phenotypes of several enteroviruses (16,20,32,41). SL I, also known as the cloverleaf, within the poliovirus (PV) 5Ј NTR is a cis element essential for stimulation of positivesense RNA transcription (2, 3). A discontinuous region encompassing SLII through SLVI constitutes a complex element known as the internal ribosome entry site (IRES) (42). The IRES stimulates translation initiation of the open reading frame by a mechanism that is unlike that utilized by the majority of cellular mRNAs. Specifically, the enterovirus genome lacks a 5Ј (m 7 GpppN) cap structure (26, 40) whi...

N-nitrosamides are known as direct-acting carcinogens at the site of their formation; they do not need any metabolic activation in vivo. The conditions leading to their formation in the stomach, and also their genotoxicity, have been thoroughly studied with some model compounds. Several reports link this type of compound to the induction of gastric cancer in human. However, only limited data are presently available about possible precursors of N-nitrosamides in foods. In the present study we found that goitrin --a naturally occurring compound in cruciferous vegetables and rape--could be easily nitrosated by treatment with nitrite under stomach conditions, yielding with loss of sulfur the N-nitroso- oxazolidone 4 (fig.). This product has a mutagenicity pattern and potency similar to that of N-nitroso-N-methyl-N'- nitroguanidine (MNNG) in the Ames Salmonella/mammalian microsome test.