One of the interesting questions concerning bacterial trainsformations is the fate of the endogenous deoxyribonucleic acid (DNA) present in the host bacterium about to produce genetically transformed progeny as a consequence of infection by an exogenous DNA agent. When a bacterium is genetically transformed, a novel DNA ageint is not simply acquired, but a homologous DNA agent previously present in the cell is effectively removed. This replacement of one agent, the eiidogenous factor, by an infectious agent homologous to it is demonstrated in reciprocal transformations. The first example of the reversibilitv of transformation was given by

No abstract

No abstract

SUMMARYFive spontaneous erythromycin resistance mutations arising independently in a pneumococcal strain have been studied. Three distinct levels of resistance are represented by these mutants (0.1, 1-0, and 10.0,ug. erythromycin per ml.). The mutations conferring resistance can be transferred to the sensitive parental strain through transforming DNA preparations. The transfer is discrete, in that the full level of resistance of the donor strain is always conferred upon the recipient. The length of time required for phenotypic expression of a mutation acquired by transformation depends on the particular marker.A mutation in a given strain may either be replaced by or combine with a different mutation transferred from a donor DNA preparation. In the case of combination, the DNA of the recombinant is capable of transferring each of the mutations as well as the entire complex of mutations possessed by the recombinant. The frequency of transfer of the complex demonstrates the degree of linkage of the separable mutations. A group of mutations in a given recombinant strain may either display antagonistic, synergistic or non-synergistic effects on the phenotype.Reverse mutations towards erythromycin-sensitivity generally involve alteration a t the originally mutated sites, or at very closely linked sites.

The induction of synchronous development of competence for genetic transformation in Streptococcus sanguis, by either endogenous or exogenous competence factor (CF), is manifested in the transient synthesis of a new set of at least 10 polypeptides, ranging from 14,000 to 51,000 in molecular weight.Eight polypeptides (E14, E16, E24, E28, E32, E37, E44, E51) appear early, and two polypeptides (L34, L42) appear 5-10 min later. One Genetic transformation in many species of bacteria is dependent on a transiently acquired physiological state, called competence, of the recipient cells. Competence confers upon cells the ability to bind native DNA from the environment. Binding culminates, after a series of events, in the integration and expression of the exogenous DNA (1-3). The competent state is elicited in some bacterial strains by the synthesis of a small protein (competence factor or CF) which triggers a synchronous response in cells to undergo competence (4,5). CF can be collected and purified from the supernatant of a competent population and, when added exogenously, can induce competence in physiologically noncompetent cells of the same or closely related species (6). These inductions require protein synthesis (7).In Bacillus subtilis, development of competence is restricted to a small, biosynthetically inactive fraction (<20%) of the cell population (8), whereas in Streptococcus sanguis (9) and S. pneumoniae (10) nearly the entire population becomes competent for a short time during exponential growth. Until recently, no significant changes in overall macromolecular synthesis (11) have been detected in the latter group of species. Although induction of new proteins during development of competence has been demonstrated (12), more recent evidence indicates that protein synthesis during the development of competence in S. pneumontae is restricted to a new set of 11 principal species (13).The publication costs of this article were defrayed in part by page charge payment. This article must therefore by hereby marked "advertisement" in accordance with 18 U. S. Macromolecular Synthesis. Cell samples removed from competence medium at various time intervals, in volumes to contain 1-2 X 108 colony-forming units (CFU) were pelleted, washed with chilled synthetic medium, and labeled for 10 min at 370C in 0.5 ml of synthetic medium supplemented with[3H]leucine (40 ,gCi/ml; 1 Ci = 3.7 X 1010 becquerels), [3H]-uridine (100,gCi/ml), or [3H]thymidine (20,MCi/ml). A portion from each sample was deposited on a filter disc (glass microfiber, GF/A). Each filter disc was then immersed in 10 ml of ice-cold 10% trichloroacetic acid for 4 hr. washed with 150 ml of 5% trichloroacetic acid and then 50 ml of ethanol, dried, and assayed for radioactivity.Competence. Cells in 0.5 ml of synthetic medium were incubated for 8 min and exposed to 1 /,tg of [3H]thymidine-labeled S. sanguis str-r43 (streptomycin-resistant) DNA (specific activity, 2.0-2.2 X 105 cpm/Ag) for 1 min. DNA uptake was terminated by addition of DNase 1 (20 ,u...