Microviridae

The Microviridae is a family of bacteriophages that infect bacteria. These viruses are characterized by their small, icosahedral capsids and single-stranded DNA genomes. The family is divided into several genera, including the well-studied Microvirus and the subfamily Gokushovirinae.

Structure

Microviridae virions are non-enveloped and have an icosahedral symmetry with a diameter of about 25-27 nm. The capsid is composed of 60 copies of the major capsid protein, arranged in a T=1 icosahedral lattice. The genome is a circular single-stranded DNA molecule, typically around 5,000 to 6,000 nucleotides in length.

Genome and Replication

The genome of Microviridae is compact and encodes a small number of proteins. These include the major capsid protein, a DNA replication initiator protein, and several other proteins involved in the assembly and maturation of the virion. Replication occurs in the cytoplasm of the host cell and follows the rolling circle replication mechanism typical of single-stranded DNA viruses.

Life Cycle

The life cycle of Microviridae begins with the attachment of the virion to the host cell surface, mediated by specific interactions between the viral capsid proteins and receptors on the bacterial surface. Following attachment, the viral DNA is injected into the host cell, where it is converted into a double-stranded form by host enzymes. The viral genome is then transcribed and translated, leading to the production of viral proteins and the assembly of new virions. The host cell is eventually lysed, releasing the progeny virions to infect new cells.

Host Range

Microviridae primarily infect Enterobacteria, but members of the subfamily Gokushovirinae have been found to infect a broader range of hosts, including Spiroplasma and Chlamydia. The host range is determined by the specificity of the interaction between the viral capsid proteins and the host cell receptors.

Evolution and Diversity

Microviridae exhibit a high degree of genetic diversity, which is reflected in the variety of host organisms they infect. This diversity is driven by the high mutation rates typical of single-stranded DNA viruses and the selective pressures imposed by the host immune system and environmental factors.

Applications and Importance

Microviridae are important tools in molecular biology and genetics due to their simple structure and well-characterized life cycle. They have been used as model systems to study virus-host interactions, DNA replication, and protein assembly. Additionally, understanding the biology of Microviridae can provide insights into the evolution of viruses and their role in microbial ecosystems.

Also see

• Bacteriophage
• Single-stranded DNA virus
• Virus replication
• Icosahedral virus

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  Genome map of the bacteriophage ΦX174 showing overlapping genes