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Yeast - an unlikely tool on the front lines of genetic engineering

By Robert C. CowenRobert C. Cowen is the Monitor's natural science editor. / October 11, 1983



Yeast - a microbe that has served humanity since prehistoric times - has acquired a new dimension of utility. It is the only organism higher than a bacterium which now can be easily manipulated by genetic engineers.

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This has made it a major new tool for studying basic genetic processes of truly higher organisms such as mammals, including man.

In fact, the fast-growing ability of genetic engineers to work with yeast has led to the creation of the first artificial chromosome. Genes - the basic genetic units that determine the nature of material organisms - have been synthesized before. To function in higher living organisms, however, whole systems of genes, together with the factors that control their operation, are organized into structures called chromosomes. Thus the creation of a functional man-made chromosome, as reported a few weeks ago by Andrew Murray and Jack Szostak of Harvard Medical School, represents a breakthrough to a larger capacity to study, and eventually to manipulate, the genetics of higher plants and animals.

Yeast may seem a humble organism for this awesome role. But seen from a human viewpoint, it is on the right side of the fundamental division of earthly life. This is the division between bacteria, whose genetic material is not confined within a nucleus (the so-called prokaryotes), and virtually all other earthly life forms, whose cells do have a nucleus (the eukaryotes). Yeast is a eukaryote. So is man.

So far, genetic researchers have had great difficulty in manipulating mammalian chromosomes. Now, with the help of yeast, they are in a position to learn more about the basics of how such genetic structures work. As Kevin Struhl , a colleague of Murray and Szostak, explains in a review in Nature, ''yeast is useful for studying many basic questions in eukaryote biology'' because yeast cells contain mechanisms and undergo processes quite similar to those of higher plants and animals. This is why genetic research with yeast is growing explosively. Struhl estimates that the number of workers in this field is doubling every two years.

Yeast has acquired this new laboratory status only within the past seven years. The techniques of genetic engineering, which have been developed with the help of bacteria, can also be used with yeast. These involve cutting and splicing the DNA molecule which carries genetic information - isolating individual genes or inserting new genes, which may be man-made. Often many copies of such genes are made using bacteria. This work has made one type of bacterium - Escheria colim - an organism that is so well understood that it is readily manipulated at the molecular level. Struhl points out that the understanding of the yeast Saccharomyces cerevisiaem now has also reached a level of sophistication where it is ''the equal of . . . E. colim.'' This is true of no other eukaryote organism.

It is too early to tell where this research is leading. But at the very least it is likely to lay bare the secrets of eukaryote chromosomes within a very few years.

Astronomers have yet another mysterious object to puzzle over. It's a cloud of gas and dark matter as big as a galaxy but with no detectable stars in it at all.

This is the first time such a mass of intergalactic matter has been detected. Thus its discovery by S.E. Schneider and a research team at Cornell University raises anew the old speculation about whether or not much of the matter in the universe exists in a form that has been difficult to detect.

Astronomers have long known that the universe is expanding. Furthermore, they have so far been unable to locate enough mass within the universe for gravitational forces eventually to halt that expansion, let alone reverse it. This has led some of them to wonder if additional mass may exist in an unseen form. This notion is supported partly by the fact that many galaxies and galaxy clusters behave in a way that indicates that they contain more matter than is visible as stars.

Such so-called ''missing mass'' may be gas, dust, burned-out stars, or other dark objects. Now the Cornell team has located a vast intergalactic cloud of gas by the radio noise it emits. The gas itself appears to have something like 800 million to 3 billion times the mass of our sun. Analysis of characteristics of the radio noise which reflect the cloud's internal motions - and hence its overall gravitational strength - suggests its total mass may be 10 to 100 times that amount. Yet there is no indication of stars. Whatever the cloud contains besides gas, it is quite dark.

The giant cloud is estimated to be 30 to 60 light-years away from Earth in the constellation Leo. If it is typical of ''unseen'' cosmic matter, this kind of object would provide at least some of the extra mass needed to halt the expansion of the universe. But before astronomers jump to that conclusion, they need to find out more about this intriguing object.