Monopartite Negative Strand RNA Genomes

Genomes of viruses in the Bornaviridae, Filoviridae, Paramyxoviridae, and Rhabdoviridae are monopartite and negative stranded. They are similar in genome organization and polymerase domain sequences, which suggests a phylogenetic relationship. The four families are now grouped taxonomically as the order Mononegavirales, although the viruses in the individual families have diverse biological properties. The pattern of genome organization suggests evolution by expansion of intergenic regions and by gene duplication, rather than by introduction of genetic information from outside. The strategies for this extension of coding capacity and refining control of gene expression include transcriptional read-through, RNA splicing, RNA editing, ribosomal frame-shifting, use of alternative initiation codons, internal initiation of transcription, overlap of open reading frames, overlap of transcription units and transcription signals, and differential codon usage.