ENCYCLOPEDIA OF Espionage, Intelligence, and Security Volume ...

ELINTcompound that can take on a negative or positive chargedepending on the surrounding conditions.) A protein inone solution might carry a positive charge in a particularmedium and thus migrate toward the negative end of thematrix. In another solution the same protein might carry anegative charge and migrate toward the positive end ofthe matrix. For each protein there is a pH in which theprotein molecule has no net charge (the isoelectric point).By varying the pH in the matrix, additional refinements inseparation are possible.Sodium dodecyl sulfate (SDS) polyacrylamide gelelectrophoresis techniques pioneered in the 1960s provideda powerful means of protein separation. Still, becauseproteins of similar mass did not always clearlyseparate into discrete bands in the gel only small numbersof molecules could be separated.The development in the 1970s of a two-dimensionalelectrophoresis technique allowed greater numbers ofmolecules to be separated. Two-dimensional electrophoresisis actually the fusion of two separate separationprocedures. The first separation (dimension) is achievedby isoelectric focusing (IEF) that separates proteinpolypeptide chains according to the arrangement of aminoacids that comprise a chain. IEF is based on the fact thatproteins will, when subjected to a pH gradient, move totheir isoelectric point. The second separation is achievedvia SDS slab gel electrophoresis, which separates themolecule by molecular size. Instead of broad, overlappingbands, the result of this two-step process is the formationof a two-dimensional pattern of spots, each comprised ofa unique protein or protein fragment. These spots aresubsequently subjected to staining and further analysis.Electrophoresis can be combined with the prior additionof a radioactive food source to the culture of bacteria.The bacteria will use the food to make new proteins, whichwill be radioactive. Following electrophoresis, the gelcan be placed in contact with x-ray film. The radioactivebands or spots will register on the film, and so will determinewhat proteins were being made at the time of theexperiment.There are many other variations on gel electrophoresiswith wide-ranging applications. These specialized techniquesinclude Southern, Northern, and Western Blotting.Blots are named according to the molecule under study. InSouthern blots, DNA is cut with restriction enzymes thenprobed with radioactive DNA. In Northern blotting, RNA isprobed with radioactive DNA or RNA. Western blots targetproteins with radioactive or enzymatically-taggedantibodies.Modern electrophoresis techniques now allow theidentification of DNA sequences that are the same, andhave become an integral part of research into gene structure,gene expression , and the diagnosis of heritablediseases. Electrophoretic analysis also allows the identificationof bacterial and viral strains and is finding increasingacceptance as a powerful forensic tool.❚ FURTHER READING:BOOKS:Birren, Bruce W., and Eric Hon Cheong Lai. Pulsed FieldElectrophoresis: A Practical Guide. San Diego: AcademicPress, 1997.Rabilloud, Thierry. Proteome Research: Two-DimensionalGel Electrophoresis and Identification Methods (Principlesand Practice). Berlin: Springer Verlag, 2000.Westermeier, Reiner. Electrophoresis in Practice. Weinheim:Vch Verlagsgesellschaft 2001.ELECTRONIC:Colorado State University. “Gel Electrophoresis of DNAand RNA.” Biomedical Hypertextbooks. January 15,2000. (5January 2003).SEE ALSOChemical and Biological Detection TechnologiesDNA Recognition InstrumentsMicrobiology: Applications to Espionage, Intelligence andSecurityThin Layer ChromatographyELINT (Electronics Intelligence).SEE SIGINT (Signals Intelligence).EM Wave ScannersIn order to observe phenomena that cannot be glimpsedthrough direct contact, for example, the activities of anisolated weapons-testing site in a hostile nation, it may benecessary to employ remote-sensing equipment and techniques.These typically involve views from the air or fromspace, which require the use of electromagnetic radiation(EMR) across a wide spectrum. Though the informationrewards can be high, intelligence services using electromagnetic(EM) scanners in space must deal with a varietyof challenges in data collection and analysis.Electromagnetic radiation from the sun. Light from the sun iselectromagnetic radiation, and it contains both electricand magnetic components. The direction of propagationfor an electromagnetic wave is mutually perpendicularwith directions of its electrical and magnetic fields, whereasthe electrical field might be thought of as the x-axis on aCartesian coordinate plane, and the magnetic field the y-axis, the direction of wave propagation is the z-axis.About 30% of the electromagnetic radiation from thesun that reaches Earth is reflected back into space unchanged,without entering Earth’s atmosphere. This is due392 Encyclopedia of Espionage, Intelligence, and Security