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.

Transcription of Ribosomal DNA in Ascaris lumbricoides Terminates at a Unique Site

E.J. Muller, F. Muller and H. Tobler

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