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Mouse L-cells contain RNA capable of hybridizing with mouse satellite DNA on nitrocellulose membranes and of competing for hybridizing sites on satellite DNA with transcript of satellite DNA prepared in vitro. RNA prepared from either whole cells or from the cytoplasm includes a fraction hybridizing with satellite DNA. That from whole cells has a half-life of 17 min, whereas that from cytoplasm is stable.

The growth of minute virus of mice (MVM) in L cells was followed by plaque assay of both cell-associated and free virus at intervals up to 36 h after infection. The major production of progeny virus occurred after incubation for 27 h and most of the virus remained cell-associated. L cells infected with MVM were pulse-labeled with 3H-thymidine for 6 h preceding induction of lysis with sodium dodecylsulfate. Two new species of DNA remained in the supernatant fractions from lysates after selective precipitation by 1 M NaCl of cellular DNA. These first appeared 17 h after infection. On the basis of sedimentation rates and response to heating and to treatment with alkali, one of these species is a hydrogen-bonded duplex molecule, which on denaturation hybridized with the single-stranded DNA of MVM virions.

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The ultraviolet circular dichroism spectra of the DNA of 10 bacterial species, all with mole percent adenine plus thymine equal to or greater than 50 were measured. The overall shapes of the spectra resembled those reported by others, but the values of the residue ellipticity at the spectral extrema departed increasingly from expected values for DNA of increasing adenine plus thymine content. For the DNA of most extreme base composition examined, that from Mycoplasma orale (mole percent adenine plus thymine, 75.6) the ratio of the ellipticity at the minimum near 245 nm to that at the maximum near 275 nm was 1.92. These values suggest that the secondary structure of DNA of very high adenine plus thymine content differs from that of DNA of less extreme base composition. A structure of the C type is postulated.

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