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Auxotrophs of Acinetobacter calcoaceticus blocked in each reaction of the synthetic pathway from chorismic acid to tryptophan were obtained after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. One novel class was found to be blocked in both anthranilate and p-aminobenzoate synthesis; these mutants (trpG) require p-aminobenzoate or folate as well as tryptophan (or anthranilate) for growth. The loci of six other auxotrophic classes requiring only tryptophan were defined by growth, accumulation, and enzymatic analysis where appropriate. The trp mutations map in three chromosomal locations. One group contains trpC and trpD (indoleglycerol phosphate synthetase and phosphoribosyl transferase) in addition to trpG mutations; this group is closely linked to a locus conferring a glutamate requirement. Another cluster contains trpA and trpB, coding for the two tryptophan synthetase (EC 4.2.1.20) subunits, along with trpF (phosphoribosylanthranilate isomerase); this group is weakly linked to a his marker. The trpE gene, coding for the large subunit of anthranilate synthetase, is unlinked to any of the above. This chromosomal distribution of the trp genes has not been observed in other organisms.

Several diaminopimelic acid (DAP)- and lysine-requiring mutants of Escherichia coli were isolated and studied by genetic, physiological, and biochemical means. The genes concerned with DAP-lysine synthesis map at several different sites on the E. coli chromosome and, therefore, do not constitute a single operon. Three separate loci affecting DAP synthesis are located in the 0 to 2.5 min region of the genetic map. The order of the loci in this region is thr-dapB-pyrA-ara-leu-pan-dapC-tonA-dapD. Two additional DAP genes map in the region between min 47 and 48, with the gene order being gua-dapA-dapE-ctr. The lys locus at min 55 determines the synthesis of the enzyme DAP decarboxylase, which catalyzes the conversion of DAP into lysine. The order of the genes in this region is serA-lysA-thyA.

Temperature-sensitive mutants of Escherichia coli K-12 which cannot form cell wall peptidoglycan at 42 C were isolated. The thermosensitive steps were characterized biochemically, and the genes coding the enzymes of peptidoglycan synthesis were mapped. These genes were in two clusters: one group, located at about 1.5 min between leu and azi, was designated as mra (murein a); the second group, located at about 77.5 min close to argH and metB, was designated as mrb (murein b, with the order metB-argH-mrb). No simple relations were found between the gene location and the order or localization of enzymes involved in the sequence of reactions of cell wall peptidoglycan biosynthesis.

The X-ray mapping procedure of Manney and Mortimer (1964) is the most widely applicable and convenient method for fine structure analysis in yeast, but suffers the disadvantage that suitable X-ray machines or gamma ray sources are very expensive. Although many other recombinogens are known, none gives a linear dose-response like X-rays and few are as convenient or give as reproducible results. Experiments with Saccharomyces cerevisiae reported in this paper show, however, that the near-ultraviolet radiation emitted by fluorescent sunlamps gives linear dose-response relations, as reproducible results as ionizing radiations, and map distances which correlate highly with those obtained by using (60)Co gamma rays. It is suggested that this convenient recombinogen may be a suitable low-cost substitute for ionizing radiations in fine structure mapping.

In this paper an analysis of genetic recombinants derived from crosses between two mutant stocks of Vibrio cholerae, strain 162, differing from one another in nutritional requirements and other characters, is presented. It is shown that parent strains possessing a fertility factor (designated as the P factor) function as gene-donors while P(-) strains (without the P factor) serve as gene-recipients. Linkage between two genetic factors (purine and valine + isoleucine) is demonstrated and the probable sequence of seven genetic factors in the chromosome of V. cholerae, strain 162, is inferred.