A prohead or procapsid is an immature viral

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...

structure formed in the early stages of self-assembly of some

bacteriophages A bacteriophage (), also known informally as a phage (), is a virus that infects and replicates within bacteria. The term is derived . Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have structures tha ...

, including the ''

Caudovirales ''Caudoviricetes'' is a class of viruses known as tailed viruses and head-tail viruses (''cauda'' is Latin for "tail"). It is the sole representative of its own phylum, ''Uroviricota'' (from ''ouros'' (ουρος), a Greek word for "tailed" + ...

'' or tailed bacteriophages. Production and assembly of stable proheads is an essential precursor to bacteriophage genome packaging; this packaging activity can be replicated ''in vitro''. The prohead structure may take a different shape from the head of a mature virion, as seen with the prohead of Bacillus subtilis phage φ29.

References

Bacteriophages {{virus-stub