Condensed DNA Structures Derived from Bacteriophage Heads

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Abstract
Bacteriophage .lambda. particles were rendered osmotically fragile by incubation, spread over hypophase and examined by EM. When water was used as hypophase, condensed structures were released from the phage heads and treatment of these with cytochrome c or several alternative proteins resulted in the release of free, relaxed DNA. Phages were pretreated with nitrogen mustard, a bifunctional alkylating agent; when the condensed structures from such phage particles were treated with protein, DNA was released in small supercoiled domains. This confirmed a previous finding that bacteriophage DNA has a supercoiled topology and suggests that the winding pattern of DNA in the phage might involve small domains of coiled DNA analogous to nucleosomes. Such a conformation could be consistent with other studies on the arrangement of DNA in phage heads if the domains have parallel axes.