The 5' termini of RNAs encoded by the transposable element copia.

The 5' termini of copia-specific RNAs in Drosophila melanogaster tissue culture cells were determined by S1 nuclease mapping and cap analysis. Both major copia RNAs share an identical set of heterogeneous 5' ends. Three major cap 1 structures M7GpppCmpUp, M7GpppCmpCp and M7GpppGmpUp together with several other minor caps were found. Almost all the 5' termini, as judged by S-1 nuclease mapping, were located either in a pyrimidine-rich part of the terminal direct repeat or apparently outside of the copia element, suggesting that a proportion of copia transcripts derive from promoters external to the genetic element.