Přehled o publikaci

The coupling of transcription and translation (CTT) is considered as one of the main gene regulation mechanisms in bacteria and plays an important role in genome stability. Recent cryo-electron microscopy (cryo-EM) studies showed the physical coupling of these two biological machineries in vitro and in vivo. Although this mechanism cannot exist in eukaryotes due to the physical separation of the nucleus and cytoplasm by a membrane, it is possible that some cytoplasmic viruses use the coupling mechanism to optimize the viral gene expression. The promising candidate is the double-strand DNA Vaccinia virus (VACV). Interestingly, VACV performs the viral genome replication, transcription and translation in infected mammalian cells within discrete cytoplasmic foci called viral factories. The initial round of viral transcription and translation during the early phase of infection occurs inside the host cytoplasm. However, in intermediate and late stage of infection the viral gene expression is carried out inside the viral factories in close association with host ribosomes. The co-localization of viral RNA polymerase with host ribosomes increases the probablity of physical interaction in a highly dense enviroment of viral factories. Additionally, in late stage of infection VACV is capable to phosporylate the RACK1 protein on small ribosomal subunit to enable the translation of 5´- polyA leader viral mRNAs. These mRNAs mostly encode viral capsid proteins. Therefore, the recent findings show that VACV has probably developed another mechanism to control the production of viral proteins by direct modification of the structure of human ribosome. Here, we present intial in vitro experiments (binding assays) to evaluate the potential interaction of VACV RNA polymerase with mammalian ribosomes mediated by specifically designed mRNAs. The primary goal is to reconstitute the CTT in vitro and use single particle cryo-EM to uncover the detailed view of the structural architecture of the viral-host CTT. Moreover, our structural analysis of human ribosomes from infected (late stage) cells indicate that roughly 70 % of ribosomes do not carry RACK1 protein. This observation indicates, that perhaps the phoshorylation of RACK1 is a signal for protein depletion in order to take a full control of host translation machinery to enable the viral protein synthesis.