[Physical mapping of the genome of phage Cd]

The effect of 7 specific endonucleases EcoRI, BamHI, BglII, SalI HindIII, XhoI, SmaI, on the genome of the phage Sd was studied. The molecular weight of the genome was estimated as 45.10(6). BamHI, EcoRI, HindIII, BglII, SmaI have altogether 15 sites of restriction SalI and XhoI do not hydrolyse the phage DNA. Fragmentation of the phage DNA in conditions of partial hydrolysis and simultaneous action of several enzymes have allowed to draw a physical man to the phage Sd DNA is more resistent to the action of restriction enzymes than DNAs from other phages. The mean size of Sd DNA fragments exceeds the statistical value almost by one order of magnitude.