prohead

A prohead or procapsid is an immature viral capsid structure formed in the early stages of self-assembly of some bacteriophages, including the Caudovirales or tailed bacteriophages.{{cite journal|last=Catalano|first=C. E.|author2=Cue, D. |author3=Feiss, M. |title=Virus DNA packaging: the strategy used by phage λ|journal=Molecular Microbiology|year=1995|volume=16|issue=6|pages=1075–1086|doi=10.1111/j.1365-2958.1995.tb02333.x|pmid=8577244|doi-access=free}} Production and assembly of stable proheads is an essential precursor to bacteriophage genome packaging; this packaging activity can be replicated in vitro.{{cite journal|last=Murialdo|first=H.|author2=Becker, A. |title=Assembly of Biologically Active Proheads of Bacteriophage Lambda in vitro|journal=Proceedings of the National Academy of Sciences|year=1977|volume=74|issue=3|pages=906–910|doi=10.1073/pnas.74.3.906|pmid=265585|pmc=430525|bibcode=1977PNAS...74..906M|doi-access=free}} 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.{{cite journal|last=Ivanovska|first=I. L.|title=Bacteriophage capsids: Tough nanoshells with complex elastic properties|journal=Proceedings of the National Academy of Sciences|year=2004|volume=101|issue=20|pages=7600–7605|doi=10.1073/pnas.0308198101|pmid=15133147|pmc=419652|display-authors=etal|bibcode=2004PNAS..101.7600I|doi-access=free}}