mbu!barani at vigyan.ernet.in mbu!barani at vigyan.ernet.in
Tue Oct 26 15:45:03 EST 1993

Todd (tkw at leland.stanford.edu) writes

"I saw a talk by Dr. Hayflick of UCSF over the summer, and at the end
of the talk he informed us that there is a sequence repeated at the end of
each chromosome.  I don't remember the exact pattern (something like
TTAGG), but it doesn't really matter.

The important thing is that this sequence was repeated a large number of
times in young cells (on the order of 100 times?).  In older cells,
however, this sequence is repeated less.  He suggested that the older a
cell, the less this sequence is repeated at the end of the chromosome.
He said that current research is looking into whether this is a
significant finding concerning cellular aging or merely a coincidence.

Has anyone else heard of this?  Has there been any progress on this research?"


	Read Burnside,E. (1984) Ann.Rev.BioChem Vol.53, p163.

(there is also a review article in Scientific American on this
and I will try to fish it out if someone is interested)

for the first discussion on telomeric repeats. The Telomere (TTAGGG)n
repeats at both ends of chromosomes in all the vertebrates. The
structure is antiparallel quadruplet and binds to an enzyme
called 'telomerase' which is the first enzyme to be discovered
that contains an RNA that is essential for its activity (this
threw out the protein-enzyme hypothesis). This enzyme is found
mostly in the germ cells (where spermatozoa production takes place)
and NOT in somatic cells. It is also known that the TTAGGG repeats
disable the shortening of chromosomes. However the cell ageing
and deletions in the (TTAGGG)n form a chicken-and-egg problem.

Others who are working on this problem include A.Rich (MIT).

Molecular Biophysics Unit
Indian Institute of Science
Bangalore 560 012 India.

barani at mbu.iisc.ernet.in

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