Enzymatic RNA Molecules and the Structure of Chromosome Ends 
organisms are linear DNA molecules. The ends of 
linear chromosomes, called telomeres, must be 
protected from degradation, and special features 
are required to ensure their replication. We are 
studying telomere structure and function, with 
special emphasis on the protein that caps off the 
ends of each chromosome. 
Most cells have only a few dozen chromosomes 
and therefore not many telomeres. We chose to 
work with a ciliated protozoan, Oxytricha nova, 
because it has 26 million miniature chromo- 
somes per cell. This facilitated our earlier purifi- 
cation of the telomeric protein and our cloning 
and sequencing of the genes that encode it. Simi- 
larities in DNA sequences in the telomeres of Oxy- 
tricha and those of higher cells, including human 
cells, give us reason to believe that our findings 
in Oxytricha will be of some generality. 
Last year we used genetic engineering methods 
to produce the two subunits of the telomere- 
binding protein in bacteria. This has now allowed 
us to assess the individual contributions of the 
two subunits to the protein-DNA complex (work 
supported mainly by a grant from the National 
Institutes of Health). It has also allowed the puri- 
fication of large amounts of the protein, enabling 
attempts to crystallize this complex, in collabora- 
tion with Steve Schultz's research group (Univer- 
sity of Colorado). If successful, crystallization 
could lead to structure determination via x-ray 
diffraction, providing an atomic-resolution pic- 
ture of the end of a chromosome. 
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