Mechanism of linear DNA circularization: formation of 'lasso'-like structures of pre-mRNA DNA copies

An electron microscopic investigation of a DNA product synthesized on the pre-mRNA template using AMV reverse transcriptase in the absence of actinomycin D revealed linear single-stranded and double-stranded molecules, and, also, double-stranded branched as well as 'lasso'-like and circular structures. Models for the formation of such DNA structures are proposed.