Baltimore scheme

The Baltimore Scheme is a classification system used to categorize viruses based on their method of viral replication. Developed by David Baltimore, a Nobel Prize-winning biologist, this system is fundamental in the field of virology and provides a framework for understanding the diversity of viral replication strategies.

Overview

The Baltimore Scheme classifies viruses into seven groups based on their genome type and the method of replication. This classification is crucial for understanding how viruses interact with host cells and how they can be targeted by antiviral therapies.

Classification

The seven groups of the Baltimore Scheme are:

Group I: Double-stranded DNA viruses - These viruses have a double-stranded DNA genome and replicate using the host cell's DNA polymerase. Examples include Adenoviridae and Herpesviridae. Group II: Single-stranded DNA viruses - These viruses have a single-stranded DNA genome. They must convert their genome into double-stranded DNA before replication. An example is Parvoviridae. Group III: Double-stranded RNA viruses - These viruses have a double-stranded RNA genome. They replicate in the cytoplasm using a viral RNA-dependent RNA polymerase. An example is Reoviridae. Group IV: Positive-sense single-stranded RNA viruses - These viruses have a single-stranded RNA genome that can serve directly as mRNA. Examples include Picornaviridae and Flaviviridae. Group V: Negative-sense single-stranded RNA viruses - These viruses have a single-stranded RNA genome that is complementary to mRNA. They require a viral RNA-dependent RNA polymerase to transcribe their genome into mRNA. Examples include Orthomyxoviridae and Rhabdoviridae. Group VI: Single-stranded RNA viruses with reverse transcriptase - These viruses, such as Retroviridae, have a single-stranded RNA genome and use reverse transcriptase to convert their RNA into DNA, which is then integrated into the host genome. Group VII: Double-stranded DNA viruses with reverse transcriptase - These viruses have a double-stranded DNA genome and replicate through an RNA intermediate. An example is Hepadnaviridae.

Significance

The Baltimore Scheme is significant because it highlights the diversity of viral replication mechanisms and provides insights into the evolutionary relationships between different viruses. It also aids in the development of antiviral drugs by identifying potential targets in the viral replication cycle.

History

David Baltimore proposed this classification in 1971, and it has since become a cornerstone of virology. His work emphasized the importance of understanding the molecular biology of viruses to combat viral diseases effectively.

Applications

The Baltimore Scheme is used in research, education, and clinical settings to:

• Classify new viruses
• Understand viral pathogenesis
• Develop vaccines and antiviral drugs

Also see

• Virus classification
• Viral replication
• David Baltimore
• Virology