[The role of the encephalomyocarditis virus type 1 proteins L and 2A in the inhibition of the synthesis of cellular proteins and the accumulation of viral proteins during infection].

INTRODUCTION: Infection of cells with encephalomyocarditis virus type 1 (EMCV-1, Cardiovirus A: Picornaviridae) is accompanied by suppression of cellular protein synthesis. The main role in the inhibition of cellular translation is assigned to the L and 2A «security¼ proteins. The mechanism of the possible influence of the L protein on cellular translation is unknown. There are hypotheses about the mechanism of influence of 2A protein on the efficiency of cap-dependent translation, which are based on interaction with translation factors and ribosome subunits. However, the available experimental data are contradictory, obtained using different approaches, and do not form a unified model of the interaction between the L and 2A proteins and the cellular translation machinery. AIM: To study the role of L and 2A «security¼ proteins in the suppression of translation of cellular proteins and the efficiency of translation and processing of viral proteins in infected cells. MATERIALS AND METHODS: Mutant variants of EMCV-1 were obtained to study the properties of L and 2A viral proteins: Zfmut, which has a defective L; Δ2A encoding a partially deleted 2A; Zfmut&Δ2A containing mutations in both proteins. Translational processes in infected cells were studied by Western-blot and the pulse method of incorporating radioactively labeled amino acids (14C) into newly synthesized proteins, followed by radioautography. RESULTS: The functional inactivation of the 2A protein does not affect the inhibition of cellular protein synthesis. A direct correlation was found between the presence of active L protein and specific inactivation of cellular protein synthesis at an early stage of viral infection. Nonspecific suppression of the translational processes of the infected cell, accompanied by phosphorylation of eIF2α, occurs at the late stage of infection. Partial removal of the 2A protein from the EMCV-1 genome does not affect the development of this process, while inactivation of the L protein accelerates the onset of complete inhibition of protein synthesis. Partial deletion of the 2A disrupts the processing of viral capsid proteins. Suppression of L protein functions leads to a decrease in the efficiency of viral translation. CONCLUSION: A study of the role of EMCV-1 L and 2A proteins during the translational processes of an infected cell, first performed using infectious viral pathogens lacking active L and 2A proteins in one experiment, showed that 2A protein is not implicated in the inhibition of cellular translation in HeLa cells; L protein seems to play an important role not only in the specific inhibition of cellular translation but also in maintaining the efficient synthesis of viral proteins; 2A protein is involved not only in primary but also in secondary processing of EMCV-1 capsid proteins.

DNA-protein cross-links in cells of internal organs of rats after fractional irradiation at various doses.

The influence of daily fractional irradiation of male Wistar rats for 30 days on DNA-protein cross-links (DPC) in spleen, thymus, and liver cells was studied. The level of DPC depended strongly on the daily dose of irradiation and the studied organ. After irradiation at dose 0.5 Gy per day increased DPC level was detected in all organs. The highest level was in the lymphoid organs and the lowest in the liver. After irradiation at dose 0.3 Gy per day DPC formation was detected only in the thymus. The data suggest the existence of a dose threshold for DPC formation during fractional irradiation.

DNA-protein cross-links in different organs of mice induced by the combined action of zinc and gamma-irradiation.

Fractional whole-body gamma-irradiation of mice at total doses of 0. 5-1.5 Gy induces increased DNA-protein cross-links (DPCs) in thymus, spleen, and brain, whereas in liver no DPCs are detected. Chronic administration of zinc ions in drinking water at concentration 10 mg/liter for 20-30 days increased DPCs in thymus, spleen, brain, and liver of mice. The combined action of zinc ions and gamma-radiation produced a significantly lower amount of DPCs than was induced by the separate action of these agents.