Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

168 Chapter 3: Proteins
ORIGIN OF REPLICATION
CELL CYCLE REGULATORS
Orc2
METHIONINE SYNTHESIS
Met31
Met32
Erd3
Met4
Swe1
Cks1
Cli1
Cdc28
Cli2
Sic1
Orc1
Orc3
Orc6
Orc5
Cdc5
Orc4
Rpt1
Met28
KINETOCHORE
Okp1
Mit2
Ctf19
Cbf1
Cep3
Cbf2
Mcm21
Mck1
F-box
proteins
YDR131
Das1
Mdm30
Skp2
Hrt3
Me130
YDR306
Dla2
Ufb1 Rcy1
Yak1
YLR224W
Grr1
Cdc4
Cdc34
E2 ubiquitinconjugating
enzyme
Ctfl3
Hrt1
Vma8
Vma4
Tfp1
adaptor
protein 1
Ram2
Ram1
Skp1
Cdc53
Vma2
VACUOLAR H + -ATPase
ASSEMBLY
adaptor
protein 2
scaffold protein
(cullin)
Figure 3–81 A map of some protein–protein interactions of the SCF ubiquitin ligase and other proteins in the yeast
S. cerevisiae. The symbols and/or colors used for the five proteins of the ligase are those in Figure 3–71. Note that 15 different
F-box proteins are shown (purple); those with white lettering (beginning with Y) are known from the genome sequence as
open reading frames. For additional details, see text. (Courtesy of Peter Bowers and David Eisenberg, UCLA-DOE Institute for
Genomics and Proteomics, UCLA.)
MBoC6 m3.82/3.74
vacuolar H + -ATPase assembly (yellow shading) are separate from its function
in the SCF ubiquitin ligase. In fact, only the remaining three functions
of Skp1 illustrated in the diagram—methionine synthesis, cell cycle regulation,
and origin of replication (green shading)—involve ubiquitylation.
3. In cross-species comparisons, those proteins displaying similar patterns of
interactions in the two protein interaction maps are likely to have the same
function in the cell. Thus, as scientists generate more and more highly
detailed maps for multiple organisms, the results will become increasingly
useful for inferring protein function. These map comparisons will be a particularly
powerful tool for deciphering the functions of human proteins,
because a vast amount of direct information about protein function can
be obtained from genetic engineering, mutational, and genetic analyses in
experimental organisms—such as yeast, worms, and flies—that are not feasible
in humans.
What does the future hold? There are likely to be on the order of 10,000 different
proteins in a typical human cell, each of which interacts with 5 to 10 different
partners. Despite the enormous progress made in recent years, we cannot yet
claim to understand even the simplest known cells, such as the small Mycoplasma
bacterium formed from only about 500 gene products (see Figure 1–10). How then