The plasmid of Salmonella typhimurium LT2

Summary Methods of clonal analysis were applied to the study of heterogeneity of the progeny after crosses of 4 donor strains (Hfr H, Hfr C, KL 16 and KL 99) with 3 recipient strains (PC 0212, AB 712 and ECK 022). Three markers were used in each cross. The distal one was the selective marker. The inheritance of two additional proximal markers characterized the heterogeneity of clones originating from particular zygotes. In most crosses the percentage of heterogeneity exceeded 30. One of the recipient strains, obtained by conjugation of the conventional strain PC 0212 with the donor Hfr H revealed unusual properties in respect to heterogeneity. Exconjugants derived from this recipient (ECK 022) and donor Hfr H and Hfr C had a heterogeneity index of about 5%. It is shown that this unusual behavior reflects a very fast process of segregation of recombinants.In crosses with the donors KL 16 and KL 99 the same recipient revealed normal indices of heterogeneity. All these data are explained assuming that there exists a specific genetic marker which determines the process of decay of merozygotes. Tentatively it is called het. Its approximate localization was deduced from specifically designed experiments, in which the heterogeneity of the progeny was found very different, when the donor KL 16 transmitted different parts of its chromosome to the recipient ECK 022.