COMPLETE DNA SEQUENCE OF YEAST |
Henahan, Access Excellence
BETHESDA, MD., (4/24/96-
A worldwide collaboration of more than 100
laboratories has accomplished a significant first in scientific
research, the sequencing of the complete genome of a complex
organism, Saccharomyces cerevisiae, otherwise known as baker's
The achievement marks the complete sequencing of the largest
genome to date - more than 12 million base pairs of DNA. I also
represents the first sequencing of an organism whose cells are
like those of humans.
"Now we know for the first time all the genes it takes to make a
simple eukaryotic cell," says H. Mark Johnston, Ph.D., associate
professor of genetics, Washington University, St. Louis.
"Yeast is a superb model for understanding the basic functions of
human cells, which have to do nearly everything yeast cells do,"
Johnston adds. "As the human genome is sequenced, we will be able
to compare human genes with those of yeast. When a similar gene
is located, its function in humans can be deduced through
experiments with yeast, which is much more amenable to genetic
This strategy already has uncovered the functions of several
human disease genes. For example, experiments with yeast revealed
that a recently discovered gene that raises the risk for one type
of colon cancer normally is involved in repairing damage to DNA.
Efforts to understand the genome of yeast began in the 1950s when
Robert K. Mortimer, Ph.D., at the University of California,
Berkeley began to genetically map all of the genes on the
organism's 16 chromosomes. The second phase began in the early
1980s, when Maynard V. Olson, Ph.D., then at Washington
University School of Medicine, created a physical map of the
yeast genome by cloning overlapping DNA fragments. This map
provided the starting point for the final phase, which has
determined the order of the approximately 12 million nucleotide
building blocks in the yeast genome.
The sequencing of the yeast genome began in 1989 under the
direction of Andre Goffeau, Ph.D., a biochemist at the Catholic
University of Louvain-La-Neuve in Belgium who coordinated a
network of more than 70 laboratories in the European Union. The
Europeans sequenced 55 percent of the genome, 17 percent was
sequenced at the Sanger Centre in England, 15 percent at
Washington University, 7 percent at Stanford University, 4
percent at McGill University in Canada and 2 percent at The
Institute of Physical and Chemical Research (RIKEN) in Japan.
"This is a major milestone in the Human Genome Project. The
spirit of cooperation among laboratories throughout the world
sped the completion by as much as two years," said Robert H.
Waterston, M.D., Ph.D., who directed the work at Washington
The group sequenced all of chromosome VIII and parts of
chromosomes IV, XII and XVI. Johnston annotated the sequences and
made them freely available in GenBank, a repository maintained by
the National Center for Biotechnology Information in Bethesda,
The yeast chromosomes were sequenced from tip to tip with no
gaps, and both strands of the double helix of DNA were analyzed,
resulting in an accuracy rate of more than 99.99 percent. Because
of the composition of the yeast genome, it is unlikely that any
other genome sequence ever will match that standard, researchers
The biggest surprise was that more than half of the 6,000 genes
uncovered during the sequencing were unknown, despite decades of
intense scrutiny by yeast geneticists. Preliminary studies
suggest that a large proportion of yeast genes code for nuclear
proteins, such as transcription factors that turn other genes on
and off. Genes for membrane proteins that ferry substances in and
out of the cell also are well represented.
The next challenge will be to figure out the precise functions of
all of the genes in the yeast genome. The European Union has
launched a systematic effort by giving each lab a set of genes to
mutate. The researchers will look at the effect of each missing
gene on the organism's day to day activities.
The yeast genome has a lot of similarities with the human genes.
Discovering the precise function of each of these genes, which
will be the next task for scientists, should help us understand
the origin and the evolution of more than forty diseases,
including colon, breast and ovarian cancers,
adrenoleukodystrophy, cystic fibrosis, ataxia telangiectasia,
amyotrophic lateral sclerosis, achondroplasia and Duchenne
muscular dystrophy. Moreover, since yeast is very largely used in
food industry, important repercussions can be expected in this
area as well.
The new findings were announced on 4/24/96 at two press
conferences in Brussels, Belgium and at the National Institutes
of Health in Bethesda, Md.
Related information on the Internet
MIPS Yeast Genome
Human Genome Project