Worm Breeder's Gazette 11(5): 35

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.

Descriptive Analysis of Some Repeated Elements

G. Naclerio and A. La Volpe

In the last few years our group has been studying the large scale 
organization of repetitive DNA sequences.  We are characterizing six 
repetitive DNA families interspersed in the genome of C.  elegans: 
RcA1, RcD1, Rc35, RcC9, RcS5 and RcB1.  We presented in CSH 1989 the 
physical distribution of our repeated elements in the genome.  Some of 
these families (RcD1, Rc35, RcC9, see also La Volpe et al.  (1988) 
Nucl.  Acids Res.  16, 82138231 ) are characterized by the presence of 
short tandemly repeated modules (satellite-like repetitive DNA).
We compared the sequence of three elements belonging to the RcA1 
family (Copy number: 161) localized on chromosomes I, II and V 
respectively; each member is 118 bp in length and the core region of 
46bp is perfectly conserved between the three.  The elements of the 
RcD1 family (present at 138 loci in the genome) are characterized by 
tandem repetitions of an extremely conserved 15bp unit.  The Rc35 is 
another satellite-like family localized at 76 loci; the tandem 
repeated module is 35bp long.  The RcC9 family described in La Volpe 
et al.  (1988) has the basic tandemly repeated unit of 10bp (and the 
same consensus of the Heat-Shock Element) and is present at 84 
positions on C.  elegans genome.  An element belonging to the RcB1 
family (copy number 57) is characterized by the presence of direct 
terminal repeats of 64 bp.
We observed that, although they are present along all the 
chromosomes, these families are not distributed completely randomly, 
but there are some regions of accumulation of elements belonging to 
different repetitive families, some of which we analyzed in detail by 
sequencing.  There is an inverse correlation between the presence of 
repetitive regions along the chromosomes and the frequency of 
recombination, that recalls the repression of legitimate recombination 
near the centromeres of Drosophila and Schizosaccharomyces pombe.