Researchers Identify Protein Important for Beginning Gene-Activation Process
Researchers at Penn State have identified the single protein that initiates the gene-activation process in yeast when it marks the start of a gene and allows the transcription process to begin. An important step toward a better understanding of the gene-activation process, the discovery also promises potential applications in the effort to combat diseases such as cancer and leukemia because a comparable protein exists in humans.
The research findings will be published in the 22 June 2001 edition of Science.
"We had known that proteins were attracted to the end of a gene in order to start the process, but the question was which protein did the work," says Jerry Workman, the Paul Berg Professor of Biochemistry at Penn State and an associate investigator with the Howard Hughes Medical Institute. "What we found was an interesting protein, Tra1, that has a human homolog, Trrap, which has been implicated as an important factor in the transformation of cells into cancer cells by several oncagene products, proteins that are active in a number of tumors."
Using an interdisciplinary approach-combining biochemical, "crosslinking," and genetic methods-the researchers studied NuA4 and SAGA, two protein complexes of a type known as histone acetyltransferase complexes, or HATs. Gene activation begins when HATs attach to a single gene on a DNA molecule. Although many different proteins comprise SAGA and NuA4, they share just one protein, Tra1.
With a mixture of experimental methods-traditional biochemical and genetic experiments as well as a "crosslinking" experiment, where the use of a purified complex helped distinguish which protein among the many was being recognized by the gene-the researchers showed that the two different complexes were recruited to the gene because they shared that same Tra1 subunit.
According to Workman, the combined approaches and the collaboration with Song Tan, assistant professor of biochemistry at Penn State, created a vibrant research atmosphere as the group worked to understand how the gene-activation process functions under normal conditions in order to provide a baseline of understanding for situations of abnormal cancerous activity.
Identifying Tra1 as the target protein that genes recruit to start the transcription process represents only a part of the researchers' findings, though. As a member of a family of large proteins-"twice the size of a nucleosome, bigger than most proteins by a long shot," Workman says-Tra1's "relatives" include some other proteins that are involved in DNA repair. In addition, the researchers believe only about 25 percent of the Tra1 protein works to fulfill responsibilities as a genetic target, and that leaves a large portion of the protein's duties unknown.
"The protein is so big that it probably does a number of different things," Workman says. "It has a domain that probably recognizes signals somehow from other cells. Also, because proteins related to Tra1 are involved in DNA repair from chemical damage or ultraviolet light, it has other potentially important responsibilities. Our DNA is constantly being repaired and if that does not happen, things such as cancer can happen quickly."
Additional collaborators in the Workman laboratory were: Christine Brown, postdoctoral fellow; LeAnn Howe, postdoctoral fellow; Kyle Sousa, undergraduate student; and Michael Carrozza, postdoctoral fellow. Stephen Alley, a postdoctoral fellow in the laboratory of Stephen Benkovic, Evan Pugh Professor of Chemistry and holder of the Eberly Family Chair in Chemistry at Penn State, provided the crucial crosslinking technology used in the studies.
The research was supported by a grant from the National Institute of General Medical Sciences. In addition, Brown, Alley and Howe receive support from the Leukemia and Lymphoma Society, the National Institutes of Health, and the Canadian Institutes of Health Research, respectively.
CONTACTS:
Jerry Workman, Penn State (814) 863-8256 / jlw10@psu.edu
Steve Sampsell, PIO, Penn State (814) 865-1390 / sws102@psu.edu