Back تصنيف بلتيمور Arabic Baltimoreova klasifikacija BS Classificació de Baltimore Catalan Baltimorova klasifikace Czech Baltimore-Klassifikation German Ταξινόμηση κατά Baltimore Greek Clasificación de Baltimore Spanish Baltimore'i klassifikatsioon Estonian Classification Baltimore French Clasificación de Baltimore Galician
Baltimore classification is a system used to classify viruses by their routes of transferring genetic information from the genome to messenger RNA (mRNA). Seven Baltimore groups, or classes, exist and are numbered in Roman numerals from I to VII. Groups are defined by whether the viral genome is made of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), whether the genome is single- or double-stranded, whether a single-stranded RNA genome is positive-sense or negative-sense, and whether the virus makes DNA from RNA (reverse transcription (RT)). Viruses within Baltimore groups typically have the same replication method, but other characteristics such as virion structure are not directly related to Baltimore classification.
The seven Baltimore groups are for double-stranded DNA (dsDNA) viruses, single-stranded DNA (ssDNA) viruses, double-stranded RNA (dsRNA) viruses, positive-sense single-stranded RNA (+ssRNA) viruses, negative-sense single-stranded RNA (-ssRNA) viruses, ssRNA viruses that have a DNA intermediate in their life cycle (ssRNA-RT), and dsDNA viruses that have an RNA intermediate in their life cycle (dsDNA-RT). Only one class exists for ssDNA viruses because their genomes are converted to dsDNA before transcription regardless of sense. Some viruses belong to more than one Baltimore group, such as DNA viruses that have either dsDNA or ssDNA as their genome.
Many virus characteristics do not define which Baltimore group they belong to but do correlate to specific Baltimore groups. This includes the use of RNA editing and alternative splicing, whether the virus's genome is segmented, the size and structure of the virus's genome, the host range of viruses, whether the virus packages replication and transcription machinery into virions, and unorthodox methods of translating mRNA into proteins. Furthermore, while Baltimore groups were not established based on evolutionary relationships, research in the 21st century has found that certain groups, such as dsRNA, +ssRNA, and many -ssRNA viruses, share common ancestry.
Baltimore classification was created in 1971 by virologist David Baltimore and initially only included the first six groups. It was later expanded to include group VII after the discovery of dsDNA-RT viruses. Since then, it has become common among virologist to use Baltimore classification alongside virus taxonomy due to its utility. In 2018 and 2019, Baltimore classification was partially integrated into virus taxonomy based on evidence that certain groups were descended from common ancestors. Various taxa now correspond to specific Baltimore groups. An extension of Baltimore classification has been proposed by virologist Vadim Agol to accommodate all possible routes of genetic information transmission.