Nucleic acids bacteria-transforming activity

In 1944, Avery, MacLeod, and McCarty [85] extracted highly polymerized deoxypentose nucleic acid from the active preparation and demonstrated that this purified DNA could transform the R cell into an S cell. Later, transformation was demonstrated with a variety of bacteria, including E. coli, Shigella parody sent erica, Bacillus proteus, Salmonella, staphylococci, tubercular bacilli, and other bacteria. Mutations induced by transforming agents cause molecular changes in the elaboration of the bacterial capsule polysaccharide, in the appearance or disappearance of enzymes, and in the development or resistance to antibiotics. 

Transformation and Transduction. Transformation factors of bacteria have produced important proof for the genetic role of DNA. Of some bacteria, e.g., the Pneumococci, different strains are known which produce different capsular material. The material (a polysaccharide cf. Chapt. XVII-7) must be regarded as one of the hereditary properties, just like hair coloration of mammals. It is possible to convert (to transform) bacteria of one type (e.g. type II) to another (e.g. type III) by treating them under certain conditions with an extract of tyjie III The active factor in the extract was prepared in pure form by Avery (1944) it is high molecular weight DNA. The assumption is that transformation is a transplantation of a gene. In the host bacterium, the transplanted nucleic acid, used in the process of transformation, acquires the capacity to induce characteristics—here the synthesis of type-specific capsular material. It also acquires in the host the capacity for identical replication, since the very same transformation factor can be isolated in quantity from a new harvest of transformed bacteria. 

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