Supercoiled infectious DNA was isolated from nuclear polyhedrosis virus infecting great wax moth Galleria mellonella L.) Covalently closed DNA molecules constitute approximately 10--30 per cent in our preparations. These molecules dissappear during storage. Electron micrographs of supercoiled and open circular molecules are presented. Length of the open rings is about 50--52 micron. Infectivity of different DNA forms is discussed.

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DNA preparations from nuclear polyhedrosis virus (NPV) of Galleria mellonella L. (GmL) were fractionated in high ionic strength neutral sucrose gradient. This procedure allowed a separation of supercoiled infectious DNA molecules with contour length of 48--52 microns from infectious open ring DNA molecule, and noninfectious linear DNA molecules of the same size. In addition a heterogeneity of supercoiled DNA molecules was detected. Covalently closed DNA molecules did not contain protein or ribonucleotide ligands which could be digested by pronase or pancreatic RNase treatment. It is concluded from data on the infectivity of different molecular forms of DNA and reassociation kinetics studies, that the genome of GmL NPV is a unique ring nucleotide sequence with a molecular weight of about 90--100 X 10(6).

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