Fundamental mechanisms of nonsegmented negative strand RNA virus transcription

 Non-segmented negative strand RNA viruses have a single negative polarity RNA genome, which encodes multiple genes including nucleprotein, envelope protein, matrix protein, RNA dependent RNA polymerase and its co-factor(s). The RNA dependent RNA polymerase transcribe mRNAs by using the nucleoprotein-encapsidated RNA as the template. The initiation and termination sites of all genes have almost consensus sequence among these all. The polymerase synthesizes positive polarity RNA following entering to the genome 3' site, and subsequently transcribes mRNA when it encounters the initiation site of the first gene. After the polymerase encounters the termination site, which is usually an UTP rich site, it switches transcription to polyadenylation, and thereafter adjacent mRNA transcription from the second initiation site starts, whereas the actual mechanism of the control of switching is unclear. By repeating such transcription mechanisms, the polymerase synthesizes all mRNA and leader RNA, which is the first synthesized RNA from extreme 3' end of genome.
 This is a basic function. Of course, there are many exceptions as much as the kinds of viruses. For example, the first initiation site is located in the rear of the second initiation site in some RNA viruses. In some cases, a termination site is not recognized by a polymerase, which produces too long mRNA that is terminated at the next termination site. To reveal parts of such exception and remained unknown mechanisms is scientist's life.