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The synthesis of acetylornithine delta-transaminase is induced by arginine and by rifampin in an arginine-inducible mutant of Escherichia coli W. A mutant of the arginine-inducible strain was isolated which is resistant to rifampin. The mutation which has brought about rifampin resistance has altered RNA polymerase and has simultaneously altered the regulation of arginine biosynthesis. Three of the enzymes of arginine biosynthesis, acetylornithinase, ornithine transcarbamylase, and argininosuccinase, show a greater rate of derepression and a 2--12-fold higher level of enzyme activity in the rifampin-resistant mutant than in the parent arginine-inducible strain. Acetylornithine delta-transaminase is no longer inducible by rifampin alone, and the level of inducibility by arginine plus rifampin has been reduced by 70%. The results indicate that RNA polymerase is involved in regulation of arginine biosynthesis in E. coli W.

Effect of the M (modifier) gene of Escherichia coli W on the expression of wild-type structural genes of four arginine biosynthetic enzymes was studied by examining enzyme activity in cell-free extracts of cultures grown in minimal medium and medium containing arginine. The mutant M gene was originally identified as causing arginine-induced synthesis of acetylornithine delta-transaminase in a strain deficient for the enzyme. The strains used in this study received the mutant M gene by recombination. Noncoordinate repression has been demonstrated for two more enzymes of the arginine regulon of E. coli W and the M(-) gene increases the degree of noncoordinate repression for the regulon. Mutation of the M gene results in altered regulation of acetylornithine delta-transaminase, ornithine transcarbamylase, and acetylornithinase. In addition, a decreased growth rate is observed. It is proposed that the M gene is a regulatory gene. A model is presented to explain the data which involves changes in operator-repressor affinity for the structural genes and possibly for the gene controlling arginyl transfer ribonucleic acid synthetase.

A new disease having a characteristic and well defined symptom complex is described as occurring in young chickens in four New England states. Tremor, principally of the head and neck, and progressive ataxia are the characteristic symptoms, either or both of which may be present in a single bird. Age at onset in field epidemics ranges from 3 days to 6 weeks, with a majority of cases reported at 3 weeks. Morbidity in commercial flocks ranges from 5 to 50 per cent; mortality in affected hatches may be 50 per cent. The disease may or may not recur in successive hatches, and in the same flock in successive years. Although birds may survive an attack of the disease, nervous symptoms persist in a majority of cases. There is no evidence that nutritional factors are involved. Normal chickens have not contracted the disease by contact with affected birds. The disease has been reproduced in normal chickens by intracerebral inoculation of brain and spinal cord from affected birds. Twenty brain-to-brain passages have been made up to the present time. The incubation period in laboratory passages ranges from 6 to 44 days with symptoms appearing usually between 21 and 28 days. The proportion of inoculated birds developing symptoms has increased with successive passages. The infective agent in the brain has survived in 50 per cent glycerine for 69 days. No organism has been cultivated. The disease has been reproduced after inoculation with bacteriologically sterile filtrates obtained with Seitz and Berkefeld N filters. Attempts to demonstrate the presence of the infective agent in the chicken embryo have been inconclusive. Chicks hatched from eggs laid by birds which had survived the disease were not infected, nor were they immune to inoculation at 6 weeks of age. The characteristic lesion of the disease consists of microscopic focal collections of glia cells, perivascular infiltration, degeneration of Purkinje's cells, and degeneration of nerve cells. Foci of infiltration are present throughout the brain and spinal cord. In the viscera of birds from field epidemics, microscopic focal infiltrations of cells of the lymphoid series are often found. Their presence is most notable in the pancreas and heart. No cell inclusions have been demonstrated.