[Electron microscopic study of the DNA products of reverse transcription]

DNA-products synthesized on pre-mRNA's from rat liver and rabbit erythroidal bone marrow cells, on rabbit globin mRNA and the RNA-templates themselves have been examined by electron microscopy. In spreading conditions providing extension of molecules the sizes of DNA-products corresponded to sizes of RNA templates. Globin mRNA, pre-mRNA as well as cDNA synthesized on these templates in the presence of actinomycine D were seen as single-stranded molecules by electron microscopy. The preparations of cDNA synthesized in the absence of actinomycine D on the pre-mRNA template were represented by double-stranded molecules along side with sigle-sranded. Up to 10% of double-stranded DNA-product appeared to be branched; all branches of such molecules had the thickness and rigidity of double-stranded structures. The possible ways of formation of branched structures are discussed.