RNA structure interactions and ribonucleoprotein processes of the influenza A virus

Dawson, Wayne K; Lazniewski, Michal; Plewczynski, Dariusz

Currently, how exactly the selection between transcription and replication is determined is not completely clear. Nevertheless, based on the images of the RNPs [42, 43] , there are some indications as to how the process works. One possible and PA). Note that this model is still under investigation and the possibility remains that replication is also done in cis. The progression of the figure is from top to bottom. (Top) The vRNP has entered the nucleus of the host cell and has separated from other vRNPs. Perhaps at this stage, the vRNP has become anchored to chromatin, though this is not specified. (Next step) The 3 0 terminus of the vRNA segment somehow unwinds and the trans-acting viral polymerase captures this free segment and begins copying the sequence in the 3 0 -5 0 direction, making an antisense copy of whatever template is present. (Next frame) The process continues with the viral polymerase somehow unwinding the vRNA þ NPs, all the while recruiting new NPs for the copy. (Next frame) When the replication is complete, the structure is eventually released. There are several steps in the trans-acting model that are not fully determined yet. The schematic is inspired from [44] and [42] . The structure of the vRNP is based on the right-handed helix in [42] ; however, it is important to remember that [43] reports a left-handed helix. (A colour version of this figure is available online at: https://academic.oup.com/bfg) explanation is that the selection is influenced by the different proportions of M1 and NP [76] . In this respect, all processes are essentially transcription and are regulated by these ratios and other factors to establish whether the product will be mRNA or cRNA/ccRNA. Another view [50, 51] is that transcription involves a single viral polymerase, the so-called cis-acting polymerase, which binds somewhere in the vicinity of the promoter region (near the 3 0 end of the RNA sequence) and copies the sequence moving in the 3 0 -5 0 direction [42] and possibly responding to splicing factors, as illustrated in Figure 1 (middle). On the other hand, replication of vRNA requires transcription by an independent viral polymerase transcribing starting from the 3 0 -most end of the negative-sense viral ssRNA sequence-the so-called trans-acting polymerase [42] (Figure 2 ).