RNA virus building blocks-miRNAs not included

Shapiro and colleagues and Rouha and colleagues were the first to independently describe recombinant cytoplasmic viruses that could successfully produce miRNAs from a pri-miRNA substrate, establishing that access to Drosha is not a limiting factor [9, 10]. Since these initial discoveries, many other cytoplasmic viruses have been demonstrated to support miRNA production; these viruses include vesicular stomatitis virus (VSV), vaccinia virus (VacV), Semliki Forest virus (SFV), turnip crinkle virus (TCV), and Sendai virus (SeV) [11–13]. When complements are not kind The last theoretical constraint that might explain the lack of miRNA production from cytoplasmic RNA viruses derives from the concept of self-targeting. Because RNA virus-produced miRNAs would be perfectly complementary to the antigenome, one would imagine that this could cause dramatic attenuation. [...]it stands to reason that the only viruses generating miRNAs are those that persist within an infected cell, and these tend to be DNA viruses or RNA viruses with DNA phases (Fig 1). While it remains possible that an acute RNA virus could benefit from the modulation of a single host mRNA, this is likely not observed because such an activity can be achieved more broadly and efficiently through use of a protein-based antagonist. [...]although initial efforts have failed to identify any obvious fitness cost from the inclusion of a single miRNA, more in-depth studies under greater selective pressures may reveal that the inclusion of a hairpin does consistently impact virus replication in a negative way.