Sinsheimer, Robert Louis WORLD OF MICROBIOLOGY AND IMMUNOLOGY516•
The hydrophilic beginning of the signal sequence,
which emerges first as the protein is made, associates with the
inner hydrophilic surface of the membrane. As the hydrophilic
region of the protein merges, it burrows into the core of the
membrane bilayer. The short hydrophilic stretch within the
signal sequence anchors in the hydrophilic region on the oppo-
site side of the membrane. Thus, the sequence provides an
anchor for the continued extrusion of the emerging protein. In
some proteins, the signal sequence can be enzymatically
clipped off the remainder of the protein. Proteins of Gram-
negative bacteria that are exported from the inside of the cell
to the periplasmic space between the inner and outer mem-
branes are examples of such processed proteins. Alternatively,
the protein may remain anchored to the membrane via the
embedded signal sequence.
The signal hypothesis has been demonstrated in plant
cells, animal cells, single-celled eukaryotes(e.g., yeast), and
in bacteria. The malfunction of the signal mechanism can be
detrimental in all these systems. In contrast, the use of signal
sequences has proven beneficial for the export of bio-engi-
neered drugs from bacteria.See alsoBacterial membranes and cell wall; Prokaryotic
membrane transportSSinsheimer, Robert LouisINSHEIMER, ROBERTLOUIS(1920- )
American molecular biologist and biophysicistBorn in Washington, D.C., Robert Sinsheimer attended sec-
ondary school in Chicago before studying at the
Massachusetts Institute of Technology (MIT). At MIT
Sinsheimer took his undergraduate degree in quantitative biol-
ogy before moving on to complete his Ph.D. in biophysics.
Sinsheimer initially accepted a faculty position at MIT but
moved to Iowa State College in 1949 to take up the post of
professor of biophysics.
Sinsheimer became a professor of biophysics at the
California Institute of Technology (Caltech) in 1957 and was
Chairman of the Caltech Division of Biology from 1968 to- During this period he conducted a series of investiga-
tions into the physical and genetic characteristics of a bacte-
riophage called Phi X 174. These breakthrough studies
illuminated the viral genetic processes. Sinsheimer and his
colleagues also succeeded for the first time in isolating, puri-
fying, and synthetically replicating viral DNA.
The bacteriophage Phi X 174 was an ideal candidate for
study because it contained only a single strand of DNA com-
prised of about 5,500 nucleotides forming approximately 11
genes. In addition it was easier to obtain samples of the bacte-
riophage DNA.
In 1977 Sinsheimer left Caltech to become a chancellor
of the University of California, Santa Cruz. One reason the
position of chancellor appealed to him was that it provided a
forum to address his concerns that had developed concerning
the social implications and potential hazards of recombinant
DNA technology and cloningmethods. Sinsheimer was one of
the first scientists to question the potential hazardous uses of
molecular biologyand the ethical implications of the develop-
ing technologies. In addition Sinsheimer became committed to
promoting scientific literacy among non-scientists.
His early years at Santa Cruz were challenging. During
his tenure the university re-established itself as a seat of
research and academic excellence. Some of Sinsheimer’s
accomplishments included the establishment of the Keck tele-
scope, the establishment of programs in agroecology, applied
economics, seismological studies, and a major in computer
engineering.
Sinsheimer also participated fundamentally in the gene-
sis of the Human Genome Project. In May 1985 Sinsheimer
organized a conference at Santa Cruz to consider the benefits
of sequencing the human genome. From these and other such
deliberations arose the Human Genome Project.
Author of more than 200 scientific papers, Sinsheimer’s
autobiography, The Strands of a Life: The Science of DNA and
the Art of Education,was published in 1994.See also Bacteriophage and bacteriophage typing;
Containment and release prevention protocol; Molecular biol-
ogy and molecular genetics; Phage geneticsSSkin infectionsKIN INFECTIONS
The skin is the largest organ in the human body. It is the front
line of defense against many types of pathogens, and remains
disease-free over most of its area most of the time. However,
breaks in the skin are particularly prone to invasion by
microorganisms, and skin infections are a relatively common
complaint. Skin infections may be bacterial, viral or fungal in
nature.
Among the more common bacterial skin infections is
impetigo, a usually mild condition caused by staphylococcal
or streptococcal bacteria. It causes small skin lesions and typ-
ically spreads among schoolchildren. Folliculitis results in
pustules at the base of hairs or, in more serious cases, in
painful boils. Often it is caused by Staphylococcusspecies. A
relatively recent manifestation called “hot tub folliculitis”
results from Pseudomonasbacteria in poorly maintained hot
tubs. Those bacterial skin infections that do not resolve spon-
taneously are treated with topical or oral antibiotics.
Among the more serious bacterial infections of the skin
is cellulitis, a deep infection involving subcutaneous areas and
the lymphatic circulation in the region as well as the skin
itself. The affected area is painful, red, and warm to the touch,
and the patient may be feverish. Cellulitis is usually caused by
bacterial invasion of an injury to the skin. Treatment includes
oral and/or intravenous antibiotics, and immobilization and
elevation of the affected area.
Viral skin infections typically show up as warts caused
by the Human Papillomavirus (HPV). Common warts usually
appear on the extremities, especially in children and adoles-
cents. Plantar warts often grow on the heel or sole of the foot,
surrounded by overgrown, calloused skin. When they develop
on weight-bearing surfaces such as the heel, plantar warts may
become painful. HPV also causes genital warts, or condylo-womi_S 5/7/03 8:20 AM Page 516