Worm Breeder's Gazette 7(1): 52

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.

The Analysis of Repetitive DNA Sequences and their Relationship to Gene Expression

K.M. Felsenstein, S.W. Emmons

The presence of interspersed repetitive DNA sequences has been shown 
to be universal in all eukaryotic genomes that have been examined.  In 
Caenorhabditis een shown that the genome is 
interspersed with short repeated sequences of an average length of 300 
bp (Emmons et al., 1980).  The function of these sequences, at present,
is unknown.  In addition, via hybridization of random genomic 
fragments back to the genome, it was shown that no single major family 
of repeated sequences exists, such as, for example, the 300,000 member 
'Alu' family of primates (Emmons et al., 1979).  The C.  elegans 
genome seems to contain many small families with on the average 10 
members or less, which are more easily studied.  It is therefore 
possible to isolate and analyze all the members of a single repetitive 
family.  By looking at the structure, organization, and possible 
expression of these sequences, it may be possible to ascertain their 
role in gene expression.
In our studies a 450bp inverted repeat was isolated from a randomly 
cloned 10 kb BamHI restriction endonuclease fragment from the Bristol 
genome.  via S1 nuclease digestion.  This sequence was shown to 
hybridize to 14 other BamHI fragments in the genome.  The fragments 
ranged in size from less than 0.7 kb to greater than 15 kb.  All the 
fragments were shown to be conserved throughout the developmental 
stages as well as in the germ line.
The inverted repeat isolated above hybridizes to Bergerac genomic 
DNA with the same repetition frequency and to the same size fragments 
as in Bristol.  In addition, hybridization was shown to C.  briggsae 
genomic DNA at three locations.  It is noted, however, that the 
original 10 kb fragment carrying the inverted repeat is not detected 
in C.  briggsae.
The inverted repeat sequence was used to screen a Bristol genomic 
clone bank in the phage vector lambda1059 for the other hybridizing 
sequences, which constitute a family of repetitive sequences.  
Preliminary EM results indicate that very few of the hybrid phages 
isolated contain any secondary structure.  This observation indicates 
that most of the family members exist as isolated repeats.  In a case 
where secondary structure can be demonstrated, the size and structure 
of the inverted repeat is quite distinct from the 450bp inverted 
repeat used to define the family.
Present experiments are concentrating on the genomic location of the 
repetitive sequences of the isolated family, that is, are they 
clustered or widely dispersed in the genome?  Sequence analysis will 
soon be undertaken, as well as an examination of the possibility that 
members of this repetitive family may hybridize to members of other 
repetitive families.  In addition, an attempt will be made to 
determine whether these sequences are transcribed.