Use of restriction endonucleases
BglII,
EcoRI,
BamHI, and
HindIII, has established that in small-headed (PIS) virions of coliphage P1, as a population, the entire genome found in big-headed (P1B) virions is represented. In addition, the origin and direction of DNA packaging are identical in P1S and P1B virions.
Communicated by J. Schell