Biology Reference
In-Depth Information
The 4.64 Mb genome of
E. coli
has been sequenced and encodes 4288 protein-
coding genes (Blattner
et al
., 1997). By comparison, the 12.1 Mb genome of
S.
cerevisiae
, which is organized into 16 chromosomes, contains 5885 protein-cod-
ing genes, ~140 ribosomal RNA genes, 40 snRNA genes and 275 tRNA genes
(Goffeau
et al
., 1996). The Saccharomyces Genome Database is available online at
http://genome-www.stanford.edu/Saccharomyces/
.
The entire 97 Mb genome of
C. elegans
has also been sequenced and represents
the first fully characterized genome of a multicellular eukaryote (
C. elegans
Sequencing Consortium, 1998). This sequence predicts a total of 19 099 protein-
coding genes and at least several hundred further genes specifying noncoding
RNAs. At least 36% of
C. elegans
proteins exhibit a match in humans whilst 74%
of characterized human proteins exhibit a match with a
C. elegans
protein. Each
C. elegans
gene has an average of five introns and the exons constitute some 27%
of the nematode genome. Sequence data are available through the
C. elegans
Genome Project Website at
http://www.sanger.ac.uk/Projects/C_elegans/
.
Comparison of the complete gene/protein sets of yeast and nematode has
revealed that for a substantial proportion of the two organisms' genes, one-to-one
orthologous relationships are identifiable (Chervitz
et al
., 1998). This suggests
that the functions of many gene products were already established in the common
ancestor of fungi and the metazoa. By contrast, most of the
C. elegans
signaling
and regulatory genes that are known or expected to be involved in multicellular-
ity have no yeast orthologue even though they may contain domain sequences
present that are in yeast (Chervitz
et al
., 1998).
The possession of the complete genome sequences of various model organisms is
proving of enormous benefit in identifying the human homologues of genes that
are shared between these organisms and humans. Thus, the expressed sequence
tags (EST) database (dbEST;
http://www.ncbi.nlm.nih.gov/dbEST/index.html
)
can be screened using model organism genes as 'probes'. An example of this
approach (termed 'cyberscreening' or '
in silico
cloning') is provided by the cloning
of five human orthologues of yeast genes encoding proteins of the mitochondrial
respiratory chain complex (Petruzzella
et al
., 1998).
Within the next 5 years, the 3200 Mb human genome sequence should also
become available (Rowen
et al
., 1997). This will permit integration of cytogenetic,
genetic, physical and transcriptional maps of the genome, information on inter-
individual polymorphic variation, and the genotype-phenotype relationship par-
ticularly in the context of complex traits. Progress made in mapping and
sequencing the human genome may be followed at the following websites:
http://www.ncbi.nlm.nih.gov/genemap98/
(National Center for Biotechnology
Information),
http://www.sanger.ac.uk/HGP
(Sanger Centre),
http://genome.
wustl.edu/gsc/index.shtml
(Washington University Genome Sequencing Center),
http://www-seq.wi.mit.edu/
(Whitehead Institute/MIT Genome Sequencing
Project) and
http://www.jgi.doe.gov/
(Joint Genome Institute). The availability of
the human genome sequence will lead to the identification of novel genes encod-
ing new proteins and the characterization of disease genes which should provide
new insights into mechanisms of disease. Comparative genome mapping will also
provide important insights into the evolution of the mammalian genome, its chro-
mosomal architecture and its genes and gene families.
