genome may be packed or sent to the nucleus for further rounds of transcription. dsDNA-RT viruses are, like ssRNA-RT, all included in the class Revtraviricetes. Two families of dsDNA-RT viruses are recognized: Caulimoviridae, which belongs to the order Ortervirales, and Hepadnaviridae, which is the sole family in the order Blubervirales. Multi-group characteristics A number of characteristics of viruses are not directly associated with Baltimore classification but nonetheless closely correspond to multiple, specific Baltimore groups. This includes alternative splicing during transcription, whether the viral genome is segmented, the host range of viruses, whether the genome is linear or circular, and different methods of translating viral mRNA. Alternative splicing Alternative splicing is a mechanism by which different proteins can be produced from a single gene by means of using alternative splicing sites to produce different mRNAs. It is found in various DNA, -ssRNA, and reverse transcribing viruses. Viruses may make use of alternative splicing solely to produce multiple proteins from a single pre-mRNA strand or for other specific purposes. For certain viruses, including the families Orthomyxoviridae and Papillomaviridae, alternative splicing acts as a way to regulate early and late gene expression during different stages of infection. Herpesviruses use it as a potential anti-host defense mechanism to prevent synthesis of specific antiviral proteins. Furthermore, in addition to alternative splicing, because cellular unspliced RNA cannot be transported out of the nucleus, hepadnaviruses and retroviruses contain their own proteins for exporting their unspliced genomic RNA out of the nucleus. Genome segmentation Viral genomes can exist in a single, or monopartite, segment, or they may be split into more than one molecule, called multipartite. For monopartite viruses, all genes are on the single segment of the genome. Multipartite viruses typically package their genomes into a single virion so that the whole genome is in one virus particle, and the separate segments contain different genes. Monopartite viruses are found in all Baltimore groups, whereas multipartite viruses are usually RNA viruses. This is because most multipartite viruses infect plants or fungi, which are eukaryotes, and most eukaryotic viruses are RNA viruses. The family Pleolipoviridae varies as some viruses are monopartite ssDNA while others are bipartite with one segment being ssDNA and the other dsDNA. Viruses in the ssDNA plant virus family Geminiviridae likewise vary between being monopartite and bipartite. Host range Different Baltimore groups tend to be found within different branches of cellular life. In prokaryotes, the large