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Gundersen, Wenche B. (Oslo University, Oslo. Norway), Kaare Jyssum, and Sverre Lie . Genetic instability with episome-mediated transfer in Escherichia coli . J. Bacteriol. 83: 616–623. 1962.—Hospital strains of Escherichia coli have been simultaneously screened for an increased mutation rate to streptomycin (Sm) resistance and to auxotrophy. Two strains were found with an increased mutation rate to Sm, but with no more than normal mutation rates in other loci tested. These loci included threonine, histidine, methionine, isoleucine-valine, resistance to tetracycline, and resistance to chloramphenicol. The genetic determinant of the new type of instability of the Sm locus has been studied. In contrast to the Treffers mutator gene, the new mutator character was not found to follow the pattern of a chromosomial factor in genetic cross. The character was found to possess the properties generally ascribed to genetic determinants of an episome nature: (i) a spontaneous loss of the character, enhanced by treatment with ultraviolet irradiation and acridine dyes; (ii) a loss which apparently is permanent; and (iii) a transfer to a mutator-negative cell by infection, both to a homologous mutator-negative mutant and to a K-12 strain. This infection is favored by the presence of the F factor in the donor.

BIOCHEMISTRY: GORINI AND GUNDERSEN 961 N-acyl-D-mannosamine 6-phosphate + PEP N-acylneuraminic acid 9-phosphate + Pi. Whether the N-acetyl-and N-glycolylneuraminic acid 9-phosphates are formed by the same enzyme remains to be established as well as the possible relationship between these substances and the biosynthesis of nucleotides containing sialic acids. 14

New type of streptomycin resistance resulting from action of the episomelike mutator factor in Escherichia coli. J. Bacteriol. 86:510-516. 1963.-Analyses have been performed to elucidate the genetic nature of the streptomycin resistance that results from the action of the previously described episomelike mutator factor in Escherichia coli. This streptomycin resistance has been found to differ from ordinary one-step streptomycin resistance. The new type of streptomycin resistance, "mutator resistance," can be lost, either spontaneously or by treatment with ultraviolet light and acriflavine. It is more stable in a K-12 strain than in the original E. coli strain 635. Mutator resistance segregates like a chromosomal marker in genetic crosses, and is located near the ordinary streptomycin locus. The locus for mutator resistance is

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