Volume 3

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

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    usual system, so that both competent and noncompetent bacteria gain the DNA; but only the competent bacteria are able to utilize its genetic information. In addition to whatever changes are necessary to permit uptake of DNA, the establishment of competence must thus include development of systems concerned with the stages of transformation succeeding uptake. Competent cells of pneumococcus possess an antigen (detected by reaction with rabbit serum) which is absent from noncompetent cells. Tomasz and Beiser (1965) observed that production of this antigen is provoked when competence factor is added to noncompetent cells. The reaction against the antigen inhibits the development of competence both in cells which develop it in culture and in cells in which its production is stimulated by addition of extraneous competence factor. This is consis tent with the idea that the competence factor acts on cells to induce competence in normal cultures, one step in the response of the cells being the synthesis of a new protein. A mutant strain of pneumococcus that does not depend upon the competence factor has been isolated by Lacks and Greenberg (1973), by selecting for cells able to be transformed in the presence of trypsin (which destroys the competence factor). These cells clearly must differ from wild type in the mechanism by which they acquire competence. Inhibition of protein or RNA synthesis during treatment with compe tence factor prevents acquisition of competence, suggesting that synthe sis of new proteins is necessary for its development. Tomasz (1970) followed the effects of inhibition of various, synthetic processes in cells at different stages of transformation: being treated with competence factor; in the competent cells before addition of DNA; and during DNA uptake. Inhibition of DNA synthesis has no effect on any of these processes. Inhibition of protein or RNA synthesis inhibits transformation when added during acquisition of competence or before addition of DNA to competent cells; it is not clear what effect it may have at the time of DNA uptake. Establishment of the competent state thus requires protein syn thesis, both in order to synthesize competence factor and then to synthe size the proteins whose production it stimulates. The same situation prevails in H.influenzae and in Streptococcus, in which Ranhand and Lichstein (1969) and Leonard (1973), respectively, found that inhibition of protein synthesis prevents the onset of competence. The importance of the cell wall in the development of competence is made clear by the results reported by Tomasz, Zanati and Ziegler (1971). Choline residues of the techoic acid component of the pneumococcal cell envelope are needed for several functions; the absence of choline results in defective cell division because daughter cells are unable to separate.