virus" is synonymous with Negarnaviricota. Negarnaviricota is divided into two subphyla: Haploviricotina, whose members synthesize a cap structure on viral mRNA required for protein synthesis, and Polyploviricotina, whose members instead obtain caps on mRNA via cap snatching. Reverse transcribing viruses Reverse transcribing (RT) viruses have genomes made of either DNA or RNA and replicate via reverse transcription. Two groups of reverse transcribing viruses exist: single-stranded RNA-RT (ssRNA-RT) viruses, and double-stranded DNA-RT (dsDNA-RT) viruses. Reverse transcribing viruses are classified in the kingdom Pararnavirae in the realm Riboviria. Group VI: single-stranded RNA viruses with a DNA intermediate The sixth Baltimore group contains viruses that have a (positive-sense) single-stranded RNA genome that has a DNA intermediate ((+)ssRNA-RT) in its replication cycle. ssRNA-RT viruses are transcribed in the same manner as DNA viruses, but their linear genomes are first converted to a dsDNA form through a process called reverse transcription. The viral reverse transcriptase enzyme synthesizes a DNA strand from the ssRNA strand, and the RNA strand is degraded and replaced with a DNA strand to create a dsDNA genome. The genome is then integrated into the DNA of the host cell, where it is now called a provirus. The host cell's RNA polymerase II then transcribes RNA in the nucleus from the proviral DNA. Some of this RNA may become mRNA whereas other strands will become copies of the viral genome for replication. ssRNA-RT viruses are all included in the class Revtraviricetes, phylum Arterviricota, kingdom Pararnavirae of the realm Riboviria. Excluding Caulimoviridae, which belongs to Group VII, all members of the Revtraviricetes order Ortervirales are ssRNA-RT viruses. Group VII: double-stranded DNA viruses with an RNA intermediate The seventh Baltimore group contains viruses that have a double-stranded DNA genome that has an RNA intermediate (dsDNA-RT) in its replication cycle. dsDNA-RT viruses have a gap in one strand, which is repaired to create a complete dsDNA genome prior to transcription. dsDNA-RT viruses are transcribed in the same manner as dsDNA viruses, but make use of reverse transcription to replicate their circular genome while it is still in the capsid. The host cell's RNA polymerase II transcribes RNA strands from the genome in the cytoplasm, and the genome is replicated from these RNA strands. The dsDNA genome is produced from pregenomic RNA strands via the same general mechanism as ssRNA-RT viruses, but with replication occurring in a loop around the circular genome. After replication, the dsDNA