Endogenous oncornaviral DNA sequences: evidence for two classes of viral DNA sequences in guinea pig cells.

The nature of the endogenous viral DNA sequences in guinea pig cells was studied by hybridization. A segment of the viral RNA (r-VRNA) hybridizing to abundant (or reiterated) DNA sequences (R-VDNA) was isolated by recycling to a Cot of 300. The hybridization of the recycled VRNA, as well as the total VRNA, was followed by determining their kinetics and by Wetmur-Davidson analysis. The kinetics of hybridization of total VRNA were complex, did not follow a second-order kinetics, and revealed two slopes by Wetmur-Davidson analysis. The recycled RNA, on the other hand, had a second-order reaction rate expected of the hybridization between a single species of RNA and DNA sequences and yielded a single straight line in a Wetmur-Davidson plot. The Cot1/2 and slope of the recycled r-VRNA was almost identical to that of the abundant VDNA sequences obtained from the hybridization data of the total VRNA. Guinea pig 28S rRNA with or without recycling was used in monitoring hybridization rate. The kinetics of hybridization of 28S RNA followed a second-order reaction and produced a single straight line by Wetmur-Davidson plot, with a second-order reassociation rate constant of 9.6 x 10(-3) liters/mol-s, a Cot1/2 of 104 mol-s/liter, and reiteration frequency of 146. There was no difference in the kinetics of hybridization of 28S RNA before and after recycling. These experiments showed that guinea pig cells contain two classes of VDNA sequences. (i) R-VDNA sequences with a second-order reassociation rate constant of 8.2 x 10(-4) liters/mol-s, a Cot1/2 of 1,219 mol-s/liter, and a reiteration frequency of 12 represent 37.5% of the viral genome. (ii) Unique VDNA sequences with a second-order reassociation rate constant of 1.2 x 10(-4) liters/mol-s, a Cot1/2 of 7,692 mol-s/liter, and a reiteration frequency of 2 represent 62.5% of the viral genome.