[Two types of structural organization of double-stranded DNA in phage particles]

Structural arrangement of linear unmodified duplex DNA in phage particles FI5 and SB1 was studied by the techniques of absorption spectrum, CD, scanning microcalorimetry. Hyperchromism is not registered for SB1 DNA in situ at 260 nm, in contrast to FI5 and other phages, but is visible at 260-290 nm. Phage SB1 had an unusual CD spectrum: intensity of the positive band at 280 nm was, practically, identical to the free SB1 DNA intensity. However, the character of SB1 DNA in situ melting in 1.5% HCHO corresponds to FI5 (and other phages) melting in situ in the presence of HCHO. Analysis of these spectral studies and calorimetry permitted one to identify the peaks on the thermograms of phages FI5 and SB1. Variability of heat capacity in the zone of phage particles destruction is supposed to be connected with DNA rearrangements.