Chemical world This week
The Top Stories UV light may cause double proton transfer mechanism for changing the genetic code of DNA 13
Scientists criticize government report that recommends ending limits on use of 2,4,5-T 15
B. F. Goodrich starts up its newprocess EPDM plant adding to the overcapacity of the U.S. EPDM industry 18
Engineering and construction firms are in a slump; capital spending patterns indicate little relief until 1973-75 23
Trace metals as possible pollut ants are now getting close scrutiny by several chemical firms 29
The Canadian government is tak ing preliminary steps to alleviate the unemployment crunch 35
July 19,1971
DNA MUTATIONS BY UV LIGHT Two biophysicists at Michigan State University, East Lansing, have found and confirmed a double proton transfer reaction initiated by ultraviolet light that they say may be a mechanism for changing the genetic code of deoxyribo nucleic acid (DNA). The scientists, Dr. M. Ashraf ElBayoumi and Dr. Kenneth C. Ing ham, point out that they have been working with the chemical 7-azaindole, not with DNA itself; their find ings are not hard evidence that the same reaction occurs with DNA. They note, however, that the 7azaindole molecule has a pair of bases similar to the base pairs found in DNA and joined by simi lar hydrogen bonds. Thus, Dr. ElBayoumi and Dr. Ingham believe it likely that the phenomenon does oc cur in DNA. In theory, the reaction goes some thing like this: A UV photon strikes one of the two bases form ing a "rung" in the twisted ladder of DNA. The photon excites the struck base to a higher energy level. Then the structure of the base pair is altered as two protons, which hydrogen-bond the bases, change positions; that is, the pro tons transfer from one base to the other. Leftover energy from the reaction is emitted as green fluores cence.
According to Dr. El-Bayoumi and Dr. Ingham, the double proton transfer theoretically can change any of the four DNA bases (adenine, thymine, guanine, and cytosine) to such an extent that they will bond with bases with which they pre viously could not bond. In a biological system, the change would usually be self-repairing. However, Dr. Ingham says, "It is conceivable that such changed bases could be sufficiently longlived to produce an error." Studies with bacteria indicate that DNA rep lication occurs at a rate of about 1000 bases per second, the MSU workers note. If the change took place during replication, just be fore the two bases separated, and lasted for even a few thousandths of a second, then the changed bases could not revert to their original forms. The code of the resulting DNA would be different, and muta tions in plant and animal cells could occur. Future work will be along two main lines, Dr. Ingham tells C&EN. "As physical chemists, Dr. El-Ba youmi and I want to explore the reaction in other model systems, to characterize it better. And as bio physicists, we want to determine just how likely it is that the same reaction really does occur in DNA," the MSU scientist says.
UV radiation may change DNA code, cause mutations
IUPAC expands interdisciplinary contacts, enlarges publications, and studies pollution problems 42
Ultraviolet radiation
Ultraviolet radiation
George Kistiakowsky receives the Priestley Medal. He'll be come professor emeritus at Har vard after 47 years of research in chemical kinetics 40
A*-C
G-C
G-C
A-C*
G*-T
G-T*
A*-C
G-T
G*-T
A-T
A-T
A-C*
Note: DNA bases, A = adenine, Τ = thymine, G = guanine, C = cytosine. Asterisk indicates new base structures which result from double proton transfer.
JULY 19, 1971 C&EN 13
