Two distinct R mutants of pneumococcus type VIIIS have been described in which the mutations leading to loss of type VIII polysaccharide production are non-allelic. A DNA extract prepared from either R strain restores the capacity to produce type VIII polysaccharide in the other strain. Autologous extracts are inert in this respect.
DNA extracts from pneumococcus type IIS when applied to the two R mutants consistently yielded a high proportion of cells transformed to type VIIIS and relatively small numbers of type IIS cells.
When extracts prepared from other encapsulated pneumococci, types IS, VIIS, XIVS, and XVIIIS, were applied to R mutant VIII-R1, a mixture of type VIIIS cells and cells corresponding to the type of the donor appeared, although the proportion of type VIIIS cells was not uniformly in excess. The same extracts applied to the second R mutant, VIII-R13, yielded transformed cells of the type of the donor only, or else transformation did not occur.
Transforming extracts of a strain of pneumococcus type IIIS gave rise only to type IIIS pneumococci when applied to either strain. Type VIIIS pneumococci were never recovered from such interactions.