Published Papers

Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III. January 1944.

Page 04 [140]

< Previous Page     Page 03 [139]

Back to Document Index Studies on the Chemical Nature of the Substan...

Next Page > Page 05 [141]

Title:	Studies on the Chemical Nature of the Substance [4 of 23]
Alternative Title:	Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III
Creator:	Avery, Oswald T.
Contributor:	MacLeod, Colin M.
Publisher:	Journal of Experimental Medicine
Date:	1944-01-00
Subject:	Cellular signal transduction
Description:	From the Journal of Experimental Medicine Vol. 79, No. 1.
Type:	Text
Format:	text/plain
Language:	en
Identifier:	avery-pg04.jpg
Source:	Master scanned with Epson GT-10000+ flatbed scanner at 600 dpi.
Rights:	http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/copyright.html
Full Text:	140­RANSFORMATION OF PNEUMOCOCCAL TYPES consequent loss of both type specificity and the capacity to produce infection in the animal body. The designation of these variants as R forms has been used to refer merely to the fact that on artificial media the colony surface is "rough" in contrast to the smooth, glistening surface of colonies of encapsulated S cells. The R strain referred to above as R36A was derived by growing the parent S culture of Pneumococcus Type II in broth containing Type II antipneumococcus rabbit serum for 36 serial passages and isolating the variant thus induced. The strain R36A has lost all the specific and distinguishing characteristics of the parent S organisms and consists only of attenuated and non-encapsulated R variants. The change S -> R is often a reversible one provided the R cells are not too far "degraded." The reversion of the R form to its original specific type can frequently be accomplished by successive animal passages or by repeated serial subculture in anti-R serum. When reversion occurs under these conditions, however, the R culture invariably reverts to the encapsulated form of the same specific type as that from which it was derived (11). Strain R36A has become relatively fixed in the R phase and has never spontaneously reverted to the Type II S form. Moreover, repeated attempts to cause it to revert under the conditions just mentioned have in all instances been unsuccessful. The reversible conversion of S;:±R within the limits of a single type is quite different from the transformation of one specific type of Pneumococcus into another specific type through the R form. Transformation of types has never been observed to occur spontaneously and has been induced experimentally only by the special techniques outlined earlier in this paper. Under these conditions, the enzymatic synthesis of a chemically and immunologically different capsular polysaccharide is specifically oriented and selectively de- termined by the specific type of S cells used as source of the transforming agent. In the course of the present study it was noted that the stock culture of R36 on serial transfers in blood broth undergoes spontaneous dissociation giving rise to a number of other R variants which can be distinguished one from another by colony form. The significance of this in the present instance lies in the fact that of four different variants isolated from the parent R culture only one (R36A) is susceptible to the transforming action of potent extracts, while the others fail to respond and are wholly inactive in this regard. The fact that differences exist in the responsiveness of different R variants to the same specific stimulus enphasizes the care that must be exercised in the selection of a suitable R variant for use in experiments on trans formation.­he capacity of this R strain (R36A) to respond to a variety of different transforming agents is shown by the readiness with which it can be transformed to Types I, III, VI, or 1IV, as well as to its original type (Type II), to which, as pointed out, it has never spontaneously reverted. Although the significance of the following fact will become apparent later on, it must be mentioned here that pneumococcal cells possess an enzyme capable of de- stroying the activity of the transforming principle. Indeed, this enzyme has been