The definition of transcription units for mRNA.

The detailed analysis of TUs with purified Ad2 DNA and the analysis of TU size for the bulk HeLa cell hnRNA compared to the size of mRNA of infected and uninfected cells supports the conclusion that mRNA in mammalian cells is generally derived by the processing of primary transcripts. In the context of this volume, these results indicate that the RNA transcription products of chromatin which are related to mRNA are longer than the mRNA itself. Proper functioning of chromatin in vitro must eventually take these results into account.