Worm Breeder's Gazette 9(2): 31

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Putative Cis-Acting Nematode 5S DNA Sequences

D.W. Nelson and B.M. Honda

Figure 1

We previously reported C.  elegans 5S rRNA gene structure, and 
demonstrated accurate, RNA pol III-specific transcription of the 
cloned 5S DNA in a homologous embryonic cell free extract.  We are 
currently manipulating this system to identify template sequences and 
extract components required for efficient transcription.  Here we 
report on the identification of potentially important, cis-acting 
template sequences.
We have constructed a set of 5' and 3' deletions of a 
transcriptionally active 5S DNA repeat, and are examining their 
transcriptional activity in the nematode cell free system.  
Preliminary results suggest that sequences upstream of the 5S rRNA 
coding region are required for transcription (see figure).  In 
contrast, X.  laevis 5S rRNA transcription (in a homologous extract) 
is relatively insensitive to 5' flanking sequence.
As an alternative way of identifying functionally important 5S DNA 
sequence elements, we have isolated and are characterizing members of 
the C.  briggsae genomic repeat families encoding 5S rRNA.  
Preliminary analysis identifies two 120 bp regions which are highly 
conserved between the C..elegans and C.  briggsae 1 kb 5S DNA repeats. 
One of these conserved regions corresponds to the 120 bp 5S rRNA; the 
other is located 300-180 bp upstream, in a transcriptionally 
dispensable region of the C.  elegans repeat (see figure).

Figure 1