Section 4 — Gene Action 



The isolation and genetical analysis of 40 

 mutant strains unable to grow on nitrate, but 

 able to use nitrite, has been described in a previ- 

 ous paper. These 40 strains involve mutations in 

 at least 6 loci. All have been shown to have 

 abnormal nitrate reductase activity, when grown 

 in conditions inducing appreciable activity in 

 prototrophs. 



These findings may be explained in several 

 ways. The conversion of nitrate to nitrite may 

 proceed through a number of intermediates, each 

 conversion being affected by a separate enzyme. 

 Alternatively, the reduction may be catalysed by 

 a single complex enzyme consisting of several 

 polypeptide sub-units, the structure of each sub- 

 unit being determined by a separate gene. It is 

 also possible that some of the loci have a regu- 

 latory function, or control the transport of nitrate 

 into the cell. 



These hypotheses are not mutually exclusive, 

 and combinations of any are possible. However, 

 it appears that the mechanism controlling the 

 conversion of nitrate to nitrite in Aspergillus 

 cannot be of the one regulator — one operon 

 type already known in bacteria. 



4.38. The Inhibitory Effect of Sucrose-Sorbose-Agar 

 on a Possible Invertase Mutant of Neurospora 

 crassa. T. H. Pittenger and T. G. Brawner 

 (Manhattan, U.S.A.). 



One of the most widely employed techniques 

 of the Neurospora investigator is the use of 0.1 

 per cent sucrose and 1 per cent sorbose to induce 

 colonial-like growth of the mycelium. Although 

 the conidial viability of many strains is quite 

 high on such media, a mutant strain has recently 

 been isolated that is inhibited by this media. The 

 inhibitory effect of conidial germination and 

 growth of this mutant is one compounded of 

 three components of the media: 0.1 per cent 

 sucrose, 1 per cent sorbose, and 2 per cent agar, 

 and the full effect is expressed only when these 

 components are autoclaved together with the 

 basic salts. Some of the characteristics of this 

 inhibition follow. If glucose is substituted for 

 sucrose in the media, there is no inhibition. In 

 the absence of sorbose there is no inhibition. The 

 sucrose-sorbose medium is not inhibitory in the 

 absence of agar. Furthermore, the inhibition may 

 be relieved if the sucrose, sorbose, and basic salts 

 are autoclaved separately from the agar and then 

 combined. Similarly, if these components are 

 autoclaved separately from the agar, and the 

 agar is then added and the mixture autoclaved 

 again, there is no inhibition. If mutant conidia 

 are germinated in liquid media supplemented 



with either sucrose or glucose and then plated on 

 sucrose-sorbose-agar medium, they do not form 

 colonies if the incubation period is less than 20 hr. 

 If, however, the pretreatment is extended to 

 24 hr or more, then inhibition is relieved. A 

 hypothesis to account for these and other obser- 

 vations will be discussed. 



4.39. Neurospora Studies of Pantothenates produced 

 by Enzymatic and by Chemical Syntheses. 

 Robert Fuerst, Lilli Li-chun-Li and Caro- 

 lyn McFall (Denton, U.S.A.). 



The in vitro synthesis of pantothenate with 

 wild type mycelium of Neurospora crassa Em 

 5256A was demonstrated by Wagner and Gui- 

 rard (1948). Acetone-dried mycelium of panto- 

 thenicless mutants were found to possess the 

 same enzyme system as wild type for the synthesis 

 of pantothenic acid from pantoyl lactone and 

 beta alanine. A new homolog of pantothenic acid 

 was prepared by incubating acetone-dried powder 

 of either Neurospora crassa pantothenicless 

 5531 A, 74A-Y153-M66, or commercial brain 

 extracts, with a substrate consisting of pantoyl 

 lactone and gamma-aminobutyric acid. The re- 

 sulting active metabolite was named gamma- 

 pantothenate. Wild type enzyme was not active 

 in the production of this compound. Purifications 

 of the active enzyme were successful, as well as 

 its separation from an enzyme cofactor. Gamma- 

 pantothenate supported the growth of Lacto- 

 bacillus arabinosus as well as a pantothenicless 

 Neurospora strain. Its chemical and physical 

 characteristics were determined. Also metabolic- 

 ally active were chemically prepared synthetic 

 calcium-gamma pantothenate and in part so- 

 dium-gamma-pantothenate. A Neurospora mu- 

 tant, able to grow on calcium-gamma-pantothe- 

 nate, was crossed to other strains. The results of 

 these matings will be discussed. 



Supported by the N.I.H., U.S. Public Health 

 Service research grant, CA 03853-06 CY. 



4.40. Glutamine Metabolism and Glutamine-requiring 

 Mutants of Neurospora crassa. E. Reich and 

 S. Silagi (New York, U.S.A.). 



A number of mutant strains of independent 

 origin, requiring glutamine for growth, have 

 been recovered from conidial populations under- 

 going "inositolless death". No complementation 

 has been observed between the six different 



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