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Transcription within a eucaryotic cell is not a process in which RNA
polymerase can freely access the DNA for either initiation or elongation of
the transcript. The DNA is associated with highly basic proteins called
histones which function to condense the DNA in an organized manner and
to facilitate accessibility of the DNA under regulated conditions. Four of
these histones, H3, H2A, H2B, H4 coil the DNA into a left-handed
supercoil and form a particle called a nucleosome. The DNA is organized
into a tandem array of these nucleosomes. Because of the strong binding
energies between these proteins and DNA, specific cellular mechanisms are required to access DNA for transcription or replication. We
are involved in a characterization of the following potential mechanisms:
1. The role of metabolic modifications such as acetylation. A common characteristic of active genes is the presence of histones that
are highly acetylated.
2. The role of topological stress in DNA. A characteristic of the transcriptional process is the formation of positive stress in advance
of the RNA polymerase and negative stress in its wake.
3. The role of accessory proteins in modulating histone-DNA interactions. Several recently characterized proteins have been shown
to function in either an ATP dependent or independent process to disrupt these interactions.
The figure illustrates a model of transcription which
encompasses these three potential mechanisms. Laboratory procedures
for testing this model involve both in vivo and in vitro
experimentation. The in vivo procedures require exposure of tissue
culture cells to radioactive and or density-labeled precursors in
order to label proteins and or DNA under conditions which alter either
replication or transcription. The dynamics of histone-DNA
interactions can be studied by this approach. The in vitro procedures
involve the assembly of individual components into a well defined
transcription system that is designed to minimize variables. By a
manipulation of the in vitro conditions, it is possible to simulate
the in vivo observations. In this way, we are able to study specific
regulatory mechanism in detail.
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"Deposition of newly synthesized histones: hybrid nucleosomes are not tandemly arranged on daughter DNA strands.",
V. Jackson
Biochemistry, 27(6), 2109-2120 (1988)
"In vivo studies on the dynamics of histone-DNA interaction: evidence for nucleosome dissolution during replication
and transcription and a low level of dissolution independent of both.",
V. Jackson.
Biochemistry, 29(3), 719-731 (1990)
"Studies on rates of nucleosome formation with DNA under stress.",
P. Pfaffle, V. Jackson.
J Biol Chem, 265(28), 16821-16829 (1990)
"In vitro evidence that transcription-induced stress causes nucleosome dissolution and regeneration.",
P. Pfaffle, V. Gerlach, L. Bunzel, V. Jackson.
J Biol Chem, 265(28), 16830-16840 (1990)
"Influence of positive stress on nucleosome assembly.",
V. Jackson,
Biochemistry, 32(22), 5901-5912 (1993)
"Dynamics of the Interactions of Histones, H2A,H2B, and H3,H4 with
Torsionally Stressed DNA", S. Jackson, W. Brooks, and V. Jackson,
Biochemistry 33, 5392-5403 (1994).
"The rapid transfer and selective association of histones H2A and H2B onto negatively coiled DNA at
physiological ionic strength.",
W. Brooks, V. Jackson.
J Biol Chem, 269(27), 18155-18166 (1994)
"Preferential Binding of Histones H3 and H4 to Highly Positively
Coiled DNA", V. Jackson,
Biochemistry 34, 10607-10619 (1995).
"Effects of Spermine and its Cytotoxic Analogs on Nucleosome Formation
on Topologically Stressed DNA in vitro", H.S. Basu, I.V. Smirnov,
H.F. Peng, K. Tiffany and V. Jackson, Eur.
J. Biochem., 243, 247-258 (1997).
"A Measurement of the Frequency of Histone Displacement During the in vitro
Transcription of Nucleosomes: RNA is a Competitor for These Histones", H.F.
Peng and V. Jackson,
Biochemistry, 36, 12371-12382 (1997).
"Formaldehyde cross-linking for studying nucleosomal dynamics.",
V. Jackson,
Methods, 17(2), 125-139 (1999)
"In vitro studies on the maintenance of transcription-induced stress by histones and polyamines.",
H.F. Peng and V. Jackson,
J Biol Chem, 275(1), 657-668 (2000)
"'Chromatin Structure: State-of-the-Art': What happens to Nuclesomes during Transcripting' in Comprehensive Biochemistry",
V. Jackson
Elshevier Publishing, In Press
"Histone release during transcription: NAP1 forms a complex with H2A-H2B and facilitates a topologically-dependent release of H3-H4 from the nuclesome."
V. Levchenko and V. Jackson
Biochemistry, In Press
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