Chromosome Structure and Function. Future Prospects

It is clear from the two symposia and the workshop
on “The Structure and Function of Chromatin”
that there has been a big advance in our understanding
of the three dimensional organization of
chromosomes at the first level of coiling of the DNA,
due mainly to the concept of the core nucleosome
particle (or ‘platysome’), although the exact location
of histone H1 and the arrangement of the linker
regions between platysomes are still in doubt. Even
less is known about the precise location of the nonhistone
proteins and the details of the higher levels of
coiling. Some 10 to 20% of the nucleosomes (the
amount depends on the tissue under study) have a
looser configuration which makes them more sensitive
to the nuclease DNase I. These ‘active’ nucleosomes
appear to include much of those stretches of DNA
which are being transcribed in any particular tissue.
In addition several lines of work suggest that
(as claimed for Escherichiu coli) the DNA in eukaryotes
is arranged in ‘domains’. The average size of these
domains is estimated, in very round terms, to be about
50000 base-pairs but the distribution of sizes about
the average is as yet unknown. Nor is the exact nature
and functional significance of these domains at all
clear though there is no lack of informed guesses
on this point. In particular one would like to know
whether the nucleosomes in a single domain are, at
any one time, all in the ‘active’ state or all in the
more compact inactive state or whether, on the other
hand, nucleosomes of both types occur at the same
time in a single domain.

http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1432-1033.1978.tb12061.x?cookieSet=1