E. L. Tatum

Novel Genotypes In Mixed Cultures of Biochemical Mutants of Bacteria

Hershey has reported (1) the occurrence of novel combinations of inherited characters in a bacterial virus. It may not be amiss to describe briefly some experimental fragments, relating to a situation in the bacterium Escherichia coli, which may be similar in some respects, Tatum, in reviewing biochemical mutations in E. co& (6), has pointed out the advantages offered by these characters for genetic analysis. In particular one may note the facility and certainty with which may be detected readily by plating heavy suspensions of the washed cells into a minimal agar medium, in which only the prototrophs will form macroscopic colonies. Their frequency is very much greater than that anticipated on the hypothesis that the prototrophs result from the coincidental occurrence, in the same clone, of reversions of two or more “loci.” Furthermore, single cultures of the same multiple mutants grown and tested under comparable conditions have not been found to

Molecular biology, nucleic acids, and the future of medicine.

It seems particularly fitting, in this symposium, to try to assess the prob able and possible impact of molecular biology and its important com ponent, the structure and function of nucleic acids, on the future of medicine. Although I attempt specific predictions with considerable trepi dation, not being qualified in either fortunetelling or medicine, I do so in the firm belief that the findings and concepts of molecular biology will play a leading role in the future of medicine. Medicine, after all, primarily involves the application of biological concepts and understanding to the health and welfare of man.

The effect of sorbose on metabolism and morphology of neurospora

Abstract 1. 1. In the presence of sorbose Neurospora grows with colonial morphology, fails to conidiate, and loses up to 60% of its dry weight after depletion of the glucose from the medium. 2. 2. After a long period of adaptation Neurospora metabolizes sorbose, apparently via sorbitol. It then grows well on sorbose, although still with colonial morphology. 3. 3. In the presence of sorbose Neurospora utilizes glucose less efficiently. Less dry weight and more CO 2 are produced, more O 2 is consumed per mg glucose used, and the incorporation of labelled glucose into cell-wall polymers and into trehalose is lower. 4. 4. This evidence suggests that the effects of sorbose on the growth and morphology of Neurospora involves a general metabolic disturbance resulting from a partial uncoupling of respiration and oxidative phosphorylation.

Inositol biosynthesis in Neurospora crassa.

Abstract 1. 1. The biosynthesis of myo -inositol in wild-type Neurospora crassa and in inositol-less mutant 896001 has been studied. 2. 2. Two enzyme preparations capable of synthesizing myo -inositol were obtained, separated and partially purified. One of them, which has been purified 360-fold, is present only in the wild-type strain and converts glucose 6-phosphate into myo -inositol phosphate, with an absolute requirement for oxidized nicotinamide-adenine dinucleotide. A phosphatase which hydrolyzes myo -inositol phosphate has been separated from this enzymatic system. 3. 3. The other enzyme, purified only 8-fold, is present both in the wild-type strain and the inositol-less mutant. This enzyme, an inositol dehydrogenase, forms myo -inositol from DL -epi- inosese -2 and reduced nicotinamide-adenine dinucleotide phosphate. 4. 4. It is concluded that in Neurospora crassa : (a) myo -inositol is normally synthesized from glucose 6-phosphate; (b) epi -inosese is not synthesized under normal conditions; and (c) epi -inosose is not an intermediate in the enzymatic conversion of glucose 6-phosphate to myo -inositol phosphate.

Genic Control of Biochemical Reactions in Neurospora

THE task of physiological genetics is that of describing gene action in chemical terms. Any such description implies, in the first place, knowledge of the chemical structure of the gene, and, in the second place, an understanding of the relationship between this chemical structure and its cellular environment. Already the first rough outlines of gene structure have been drawn. Terms such as nucleic acid, polypeptide chain, prosthetic group and crystalline virus have by now found comfortable places in the genetical vocabulary. It is the second aspect of the general problem that is the subject of the discussion this afternoon, however, and more particularly, that phase of it dealing with the role of the gene in the physiology of the organism. There is recorded in the literature a sufficient number of instances of mutations affecting the normal biochemistry of the organism to indicate that the gene exercises an important function in metabolism. The loss, through gene mutations, of the ability to form coat color pigments in mammals (Wright, 1941) and eye color pigments in Drosophila (Ephrussi, 1942) has, in particular, been investigated. Genic control of various processes involved in the production of flower pigments has also been extensively studied (Lawrence and Price, 1940). One of the clearest cases of genic control of a more or less definable chemical reaction, and also the first one to be recorded, is in the disease of mnan known as alcaptonuria (Garrod, 1923). Here the ability to oxidize hoinogentisic acid is lost, and large quantities of it are excreted in the urine. The genealogies of alcaptonurics indicate that they differ from the normal by a single recessive gene. Studies such as these have been of the greatest value in furthering our knowledge of the gene as a physiological

An Unfortunate Event

After Dement and Kleitman (1) first described a low-voltage, fast electroencephalographic sleep cycle in humans, the same type of activity was described in cats by Dement (2) and later by Jouvet et al. (3). We have duplicated this desynchronized sleep electroencephalogram in five of our cats that have been implanted with bipolar electrodes in various deep and surface structures of the brain. These animals have been trained to go to sleep in a sound-proofed room. Behavioral and electroencephalographic arousal thresholds in response to stimulation of the reticular formation are then recorded. The cats exhibited the normal behavioral and electroencephalographic patterns associated with going to sleep, and after 60 or more minutes of complete isolation they drifted into a very high frequency (40 to 50 per second), low amplitude, desynchronized activity (Fig. iB). As described by Jouvet et al. (3), the animals were completely relaxed and deeply asleep. Especially noticeable are the occasional convulsive limb twitches. One of the cats slept with the eyes partially open during this phase. She showed marked nystagmic movements of the eyeball under relaxed nictitating membranes. Although Dement (4) states that he cannot detect changes in arousal threshold between the fastor slow-wave sleep stages, we have found increases in the reticular formation behavioral arousal thresholds of from 1 to 2.5 volts in all of our cats (Fig. 1). This finding confirms Jouvets report (3) of increased auditory and reticular arousal thresholds during this sleep period. One aspect of this desynchronized sleep stage not yet reported is shown in Fig. 1C. Recticular stimulation that

Sorbose transport in Neurospora crassa

Abstract 1. 1.|The transport of sorbose into late log-phase cultures of Neurospora crassa does not occur against a concentration gradient, but obeys saturation kinetics, is energy-requiring, and is competitively inhibited by glucose. 2. 2.|The apparent K m for transport is 116 mM, and the maximal velocity is 0.92 μmol/mg dry wt. per h. 3. 3.|Adding glucose to cells which have been previously equilibrated with sorbose causes the counterflow of sorbose against a concentration gradient.

THE BIOSYNTHESIS OF ANTIBIOTIC POLYPEPTIDES

This chapter discusses the biosynthesis of antibiotic polypeptides. Certain common features of antibiotic polypeptides are relevant to their mode of biosynthesis. Peptide antibiotics are produced only during a limited period of the life cycle of the producing organism, after the end of the logarithmic phase of growth, when certain nutrients essential for growth, have disappeared from the medium. A wide variety of unusual amino acids, which do not occur in proteins, are found in antibiotic polypeptides. This might be considered as a theoretical argument in favor of a mode of biosynthesis different from that of proteins. A number of the “unnatural” amino acids could have resulted from the modification of normal amino acids, for instance by methylation, after their incorporation into a peptide chain. Antibiotic polypeptides occur as groups, or “families,” of structurally related molecules, differing from one another by only a single amino acid. Such is the case for the bacitracins, the tyrocidines, and the vernamycins.