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Roger D. Kornberg*
Stanford University School of Medicine, Stanford, CA 94305-5400

I

am deeply grateful for the honor
bestowed on me by the Nobel
Committee for Chemistry and the
Royal Swedish Academy of Sciences. It is an honor I share with my
collaborators. It is also recognition of
the many who have contributed over the
past quarter century to the study of
transcription.
TheNucleosome
My own involvement in studies of transcription began with the discovery of the
nucleosome, the basic unit of DNA coiling in eukaryote chromosomes (1). Xray studies and protein chemistry led me
to propose the wrapping of DNA
around a set of eight histone molecules
in the nucleosome (Fig. 1). Some years
later, Yahli Lorch and I found that this
wrapping of DNA prevents the initiationof transcription in vitro (2). Michael
Grunstein and colleagues showed nucleosomes interfere with transcription in
vivo (3). The nucleosome serves as a
general gene repressor. It assures the
inactivity of all of the many thousands
of genes in eukaryotic cells except those
whose transcription is brought about by
specific positive regulatory mechanisms.
What are these positive regulatorymechanisms? How is repression by the
nucleosome overcome for transcription?
Our recent work has shown that promoter chromatin is transformed from a
static to a dynamic state upon gene activation (4). Nucleosomes are rapidly removed and reassembled in the activated
state. Promoter DNA is made transiently available for interaction with the
transcription machinery.
RNA Polymerase II (Pol II)Transcription
Our studies have focused on the RNA
pol II transcription machinery. Pol II is
responsible for all messenger RNA synthesis in eukaryotes. As the first step in
gene expression, pol II transcription is
an end point of a great many signal
transduction pathways. The intricate regulation of pol II transcription underlies
cell differentiation and development.
Because nucleosomes areremoved
from promoter DNA for transcription in
vivo, we and others have been able to
fractionate the components of the transcription machinery guided by transcription assays performed with naked DNA
in vitro. Robert Roeder and colleagues
initiated the isolation of pol II transcription proteins from human HeLa cell
extracts (5). This effort was brought to
www.pnas.org cgi doi 10.1073pnas.0704138104

Fig. 1. The nucleosome, the fundamental particle
of the eukaryote chromosome. Schematic shows
the coiling of DNA around a set of eight histones in
the nucleosome, the further coiling in condensed
(transcriptionally inactive) chromatin, and uncoiling for interaction with the RNA polymerase II (pol
II) transcription machinery.

fruition by Ronald and Joan Conaway,
who took advantageof the greater
abundance of starting material available
from a rat liver extract (6). At Stanford,
we isolated the pol II machinery from
yeast, in work begun by Neal Lue in
1987, who solved the longstanding problem of preparing an extract active in pol
II transcription from yeast (7). In retrospect, our pursuit of the problem in
yeast was a fortunate choice. It proved
crucial forunraveling both the structure
and regulation of the pol II machinery.
There were serious doubts when we began whether findings in yeast would
prove relevant to human cells. But,
upon fractionation of yeast and mammalian systems, the results were the same.
Both systems comprise six proteins:
pol II, and five general transcription factors, known as TFIIB, -D, -E, -F, and
-H (8). Pol II is capable ofunwinding
DNA, synthesizing RNA, and rewinding
DNA. But pol II alone is incapable of
recognizing a promoter and initiating
transcription. For these essential functions, the participation of the general
transcription factors is required.
Mediator of Transcriptional Regulation
It was, at first, thought the set of six
proteins constituted a complete tranPNAS

scription system, that it...