Biologists discover keys to the building blocks of organic life

Biologists who study basis of organic life are uncovering the basic roles played by specific molecular structure and composition. Two quite different lines of research reported in the journal Nature illustrate this.

* US and Swiss molecular biologists have discovered a DNA fragment - a specific sequence of genetic instructions - that appears to be common to such disparate organisms as yeast and man. Involved in embryonic development, it may have arisen early in the evolution of life on this planet.

* Meanwhile, at the Massachusetts Institute of Technology (MIT), a research team has elucidated the structure of molecules on the surface of the so-called T cells, which counteract viruses, bacteria, or other alien cells that may invade an animal's or human's body. The structural arrangement of these molecules enables T cells to carry out their defense. This sheds new light on the puzzle of how the immune system works.

Allen Laughon and Mathew P. Scott of the University of Colorado have studied the genetic control of insect development. Long chains of genetic information, encoded in DNA, govern formation of such different structures as abdomen, thorax , or antennae. Although the researchers still do not fully understand how this control works, they have identified a short sequence of DNA-encoded instructions - a fragment of a gene - which appears always to be involved. Furthermore, this set of instructions appears to be involved in the development of a variety of other types of organisms.

John C. W. Shepherd and co-workers at the University of Basil in Switzerland report evidence of this in yeast. They have also found evidence of the same gene fragment in beetles, chickens, earthworms, frogs, mice, and humans.

This particular set of instructions may have arisen early in the evolution of organic life itself. Its exact genetic function has yet to be elucidated. However, Harvard University biochemist Gary Struhl, in commenting on the reports in Nature, observed that the discovery may ''prove to be a major breakthrough in understanding vertebrate development.''

The work on T cells, which was done by Herman N. Eisen, Susumu Tonegawa, and colleagues at MIT, may have more practical implications. It involves two linked chains of amino acids called the alpha and beta chains. The structure of the beta chain had already been described. Now the MIT group has delineated the alpha chain structure and shown how the molecules are linked. Together they form a ''receptor'' site which enables T cells to recognize foreign invaders.

As the T-cell mechanisms are better understood, immunologists may be able to improve bodily defense against malignant cells, according to Tonegawa. They also may learn how to control T-cell activity and aid the acceptance of surgically transplanted organs, which T cells now may attack as ''foreign.''

The ability of microbiologists to isolate, analyze, rearrange, and sythesize the basic molecules of organic life has thus become a powerful tool to decipher some of the subtlest modes by which that life functions.