2.5 - 3.0 nm
||Purohit PK et al., Forces during bacteriophage DNA packaging and ejection. Biophys J. 2005 Feb88(2):851-66. p.852 left column 2nd paragraphPubMed ID15556983
||Rau, D. C., B. Lee, and V. A. Parsegian. 1984. Measurement of the repulsive force between polyelectrolyte molecules in ionic solution: hydration forces between parallel DNA double helices. Proc. Natl. Acad. Sci. USA. 81: 2621–2625.PubMed ID6585818
||p.852 left column 2nd paragraph:"DNA is highly compressed inside bacteriophage capsids, and the resulting forces have important effects on the phage life cycle, as revealed in several experiments. One early experiment which shed light on the possible role of the forces associated with packaged DNA is that of Earnshaw and Harrison (1977), who characterized the tight packaging of DNA in viral capsids by the distance ds between strands (~2.8 nm in full capsids BNID 111589), and by Feiss et al. (1977), who identified limits on the amount of DNA that can be packaged into a ?-capsid. Feiss et al. (1977) found an upper limit barely above the wild-type genome length, and suggested that adding more DNA makes the capsid unstable. Rau et al. (primary source) made measurements on large volumes of nonviral DNA that showed that ds values in the range of 2.5–3.0 nm correspond to a pressure of several tens of atmospheres."