majority of viruses are dsDNA viruses, and a significant minority are ssDNA viruses. Prokaryotic RNA viruses, in contrast, are relatively rare. Most eukaryotic viruses, including most animal and plant viruses, are RNA viruses, although eukaryotic DNA viruses are also common. By group, the vast majority of dsDNA viruses infect prokaryotes, ssDNA viruses are found in all three domains of life, dsRNA and +ssRNA viruses are primarily found in eukaryotes but also in bacteria, and -ssRNA and reverse transcribing viruses are only found in eukaryotes. Linear vs circular genomes Viral genomes may be either linear with ends or circular in a loop. Whether a virus has a linear or circular genome varies from group to group. A significant percentage of dsDNA viruses are both, ssDNA viruses are primarily circular, RNA viruses and ssRNA-RT viruses are typically linear, and dsDNA-RT viruses are typically circular. In the dsDNA family Sphaerolipoviridae, and in the family Pleolipoviridae, viruses contain both linear and circular genomes, varying from genus to genus. RNA editing RNA editing is used by various ssRNA viruses to produce different proteins from a single gene. This can be done via polymerase slippage during transcription or by post-transcriptional editing. In polymerase slippage, the RNA polymerase slips one nucleotide back during transcription, inserting a nucleotide not included in the template strand. Editing of a genomic template would impair gene expression, so RNA editing is only done during and after transcription. For ebola viruses, RNA editing improves the ability to adapt to their hosts. Alternative splicing differs from RNA editing in that alternative splicing does not change the mRNA sequence like RNA editing but instead changes the coding capacity of an mRNA sequence as a result of alternative splicing sites. The two mechanisms otherwise have the same result: multiple proteins are expressed from a single gene. Translation Translation is the process by which proteins are synthesized from mRNA by ribosomes. Baltimore groups do not directly pertain to the translation of viral proteins, but various atypical types of translation used by viruses are usually found within specific Baltimore groups: Non-canonical translation initiation: Viral initiation of translation: used primarily by +ssRNA and ssRNA-RT viruses, various viruses have evolved mechanisms to initiate translation, such as having internal ribosomal entry sites to allow for cap-independent translation, having downstream hairpin loops that allow for cap-dependent translation in the absence of an eIF2 initiation factor, and initiation at a CUG or other