Worm Breeder's Gazette 11(1): 29
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have investigated the termination of transcription of the ribosomal genes in Ascaris des (var. suum). Nuclease protection experiments with total RNA and 40S precursor rRNA isolated from different tissues revealed a unique 3' end of the primary transcripts, identical to the 3' end of the 28S rRNA. These results are in agreement with those obtained using our homologous, cell-free in vitro transcription system. Supercoiled miniplasmids, comprising the promotor region upstream, and variable sequences containing the 3' end of the 28S rRNA gene downstream, were incubated under standard transcription conditions. These constructs were able to direct correct and unique 3' end formation at a site identical to that observed in vivo. Very short incubation times already result in the formation of this unique band, indicating, that the 3' end is formed by a real termination event rather then by the processing of a longer transcript. Furthermore, miniplasmids with deletions at the 3' end formation site, initate correctly but lose their ability of transcription termination. Obviously, the termination site is unique within the rDNA repeat and is located at the very end of the 28S rRNA gene.