SUMMARY : Certain single-gene acetate-requiring mutants of Neurospora crassa (ac) are deficient in their ability to oxidize pyruvate directly, but can decarboxylate pyruvate to acetaldehyde and can form ethanol. The growth characteristics of the nc mutants indicate that they can form acetate from glucose or ethanol. ac Mutants are inhibited by glucose or sucrose. This glucose inhibition is relieved by the singlegene suppressor mutations sp and car which lower the activity of pyruvic carboxylase, decrease the amount of ethanol formed and permit some growth of ac sp and accar strains in absence of added acetate. The sp mutation also lowers ethanol dehydrogenase activity, but this activity can be partially restored by growth of sp strains in the presence of ethanol. As a result of the nearly complete block in their pyruvate metabolism, ac sp strains are forced to metabolize glucose by pathways which produce more of the initial respiratory CO, from the C-1 carbon of glucose.While genetic theory is reticent about the embodiment of the gene (Pontecorvo, 1952) there is little doubt that the physiological effects of genes are mediated via enzymes. Genes, individually and en masse, control the rates of the step reactions from which multi-enzyme systems (Dixon, 1949) are built up, and in so doing determine the metabolic pathways chosen by the organism. I n many instances gene mutation causes the block, complete or incomplete, of a step reaction; the consequence of such a block is the accumulation of precursors and the appearance of a growth requirement for the product of the blocked reaction (Beadle, 1945).The commonest use for genetic mutants in biochemistry is the definition of routes of biosynthesis by a study of the growth requirements induced and the identification of the precursors accumulated (Horowitz, 1950). As interesting, perhaps, are the inhibitions produced by the accumulated precursors or by ' abnormal ' products derived from these precursors (Emerson, 1949;Bonner, 1946). If genes do control the rates of step reactions, it should be possible with a second mutation to relieve an inhibition induced by an initial mutation, if the second mutation prevents the formation of the inhibitor. Such relief by a second mutation would be denoted, genetically, as a suppressor or modifier effect and would be one of the many instances in which the effects of two co-existing mutant genes are not merely additive. The gene interaction in such a situation would not be the simple interaction of two genes present in the nucleus but would, rather, express the interaction of the enzymic reaction systems present in non-genic parts of the cell; such interactions would further demonstrate the interdependence of the biochemical reactions of the organism. These investigations demonstrate an example of gene interaction in wellknown metabolic pathways and indicate that the selection of one of several alternate pathways is here under genetic control; all this would again emphasize the importance to genetical theory of inhibition by naturall...
The characteristics of eight mothers of ten infants born with typical features of the fetal alcohol syndrome (FAS) are presented. These chronic alcoholic mothers have poor obstetric histories, tend to have poor or no prenatal care and may repeat pregnancies which result in infants with FAS. Family planning counseling appears unhelpful.
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