Amplification of polyadenylated nontranslated small RNA sequences (POLADS) during superinfection correlates with the inhibition of viral and cellular protein synthesis.

The production and the role of POLADS in cells infected with vaccinia virus (VV) was studied in doubly infected HeLa and L cells. In cells first infected with VV followed by superinfection with UV-irradiated virus (VVuv), referred to as VV + VVuv, the course of viral polypeptide synthesis was not significantly altered. However, if cells were first infected with VVuv, followed by superinfection with VV, referred to as VVuv + VV, both host and viral polypeptide synthesis was compromised. Labeling of such infected cells with 3H-adenosine revealed that infection with VVuv or VVuv + VV, caused an amplification of incorporation of label both in the large and small size class RNAs compared to RNAs obtained from a normal infection. On the other hand, labeling of cells with 3H-adenosine which were infected with VV + VVuv, caused no significant change in the labeling pattern of large and small size class RNAs compared to labeled RNAs from normal infection. The large size class RNAs isolated from infection with VVuv or VVuv + VV, were translated in the reticulocyte lysate cell-free system much more productively compared to the same size RNAs obtained from normal infection. When these large size class RNAs were added together with HeLa cell mRNAs to the cell-free translational system, competition between the two types of mRNAs ensued. The small size class RNAs (POLADS) isolated from infection with VVuv or VVuv + VV, had little translational activity, but when added together with HeLa cell mRNAs, caused a striking inhibition of HeLa cell mRNA translation which was more pronounced than the inhibition caused by the small size class RNAs obtained from normal infections. POLADS obtained from infection with VV or VV + VVuv inhibited HeLa cell protein synthesis to the same extent and were about two times less active than the POLADS obtained from infection with VVuv or VVuv + VV. These results demonstrate that if cells are first infected with normal virus, the superinfecting UV-irradiated virus has little or no effect on the course of VV replication, suggesting that the production of POLADS under these conditions is regulated. However, when cells are first infected with VVuv, POLADS production is amplified to an "abnormal" level, thus, both viral polypeptide synthesis and replication of the superinfecting VV is compromised resulting in lower yields of virus.