Group Representatives
Negative-sense single-stranded RNA viruses include pathogens causing numerous significant human and animal infections. According to viral taxonomy, this group includes the following families:
- Arenaviridae
- Bornaviridae
- Rhabdoviridae
- Paramyxoviridae
- Orthomyxoviridae
- Filoviridae
Despite morphological differences, all these agents share a common genetic organization: their genome is represented by a negative-sense, or "minus strand", RNA, which dictates a unique pattern of interaction with the infected cell.
Infection Initiation and Entry
The reproductive cycle begins with the successful attachment of the virion to the target cell. This process can be divided into three consecutive stages:
- Adsorption. The virus recognizes specific receptors on the surface of a susceptible cell. Binding is mediated by surface glycoproteins located in the outer viral envelope.
- Penetration. Following successful adsorption, the virion envelope fuses with the host plasma membrane.
- Uncoating. As a result of membrane fusion, the internal contents of the virus are released directly into the cytoplasm. The genomic minus-strand RNA is freed from protective protein structures, preparing for the next and most crucial step.
Genome Expression: The Role of RNA Polymerase
The primary challenge for negative-sense RNA viruses is that their genomic (-)RNA is non-coding. Host cell ribosomes cannot "read" it to synthesize proteins. Therefore, a critically important requirement is the presence of a pre-formed enzyme within the virion—virion RNA-dependent RNA polymerase.
This exact enzyme carries out transcription—transforming the genomic "minus strand" into complementary "plus strands". During this process, two functionally distinct molecules are produced:
- Subgenomic copies (plus strands). These act as messenger RNA (mRNA). These shortened molecules travel to cellular ribosomes, where they serve as templates for translation—the synthesis of new virus-specific proteins.
- Full-length copies (plus strands). These represent the full-length antigenome. Their task is to serve as an intermediate template for subsequent replication, i.e., generating new generations of genomic minus-strand RNA.
Virion Assembly and Release
When a sufficient amount of newly synthesized viral proteins and fresh copies of genomic (-)RNA accumulate in the cytoplasm, the formation of new virions begins. Taking Paramyxoviruses as an example, this mechanism proceeds as follows:
- New genomic RNA strands combine with structural proteins to form a nucleocapsid.
- The assembled nucleocapsid interacts with a specific matrix protein (M-protein), which acts as a bridging link.
- The entire complex is directed toward the inner leaflet of the plasma membrane—specifically to areas already modified by embedded viral surface glycoproteins.
- Virion release occurs via budding. The virus evaginates a patch of modified cell membrane, pinches off, and thereby acquires its final outer lipid envelope.