Scientists have cloned a gene that participates in the cellularresponse to the contaminant dioxin, a finding that may leadto better tests to identify the carcinogenic risks of the toxin.

Researchers at the University of California, Los Angeles,describe the finding in the May 17 issue of Science.

Dioxin is one of a family of environmental contaminants thatactivate cellular enzymes called P450 cytochromes. Thecytochromes detoxify dioxin.

When dioxin binds to its receptor (the aryl hydrocarbon, or Ah,receptor), it is carried into a cell's nucleus. There the dioxin-receptor complex binds to the DNA and triggers the expressionof P450 enzymes.

The UCLA scientists now report that a second protein, calledArnt (Ah receptor nuclear translocator) must bind to thedioxin-receptor complex for P450 activation to occur.

This interaction also suggests that dioxin concentrations mustreach a threshold amount before the compound causes cancer.Scientists speculate that dioxin carries out its cancer-causingactivities by disrupting the regulation cells normally exert onthe expression of proteins such as P450 cytochromes and cellgrowth factors.

The Environmental Protection Agency has commissionedscientists to develop an assay based on dioxin's interactionwith its receptor. The EPA uses a standardized carcinogenicassay that dioxin experts consider obsolete, said LeslieRoberts in an accompanying Science article.

ImmunoSystems Inc. of Scarborough, Maine, is developing amonoclonal antibody-based assay to detect environmentalcontaminants such as dioxin and polychlorinated biphenyls.


Scientists at the University of California, Santa Barbara, haveshown that amino acid differences in visual proteins mayexplain variations in the ability of people to distinguish redand green colors.

The results may help uncover the mechanisms leading to colorblindness, an X-chromosome-linked genetic defect.

The researchers, reporting in the May 17 issue of Science,compared eight monkey and human cone photopigment proteins,which are 96 percent to 98 percent identical. Three amino acidsubstitutions each contributed to shifting a pigment'ssensitivity toward the color red. The authors speculate thatvariations in red-green color vision are dictated by which conephotopigment gene variants are inherited. -- CTV

-- Carol Talkington Verser, Ph.D. Special to BioWorld

(c) 1997 American Health Consultants. All rights reserved.