SULPHONAMIDE RESISTANCE IN PnEUMOCOCCI 185 



formation, as indicated in Table I. This result has been 

 repeatedly observed, with different recipient strains and 

 different DNA preparations. 



Further genetic analysis of the system was made by isolat- 

 ing and testing several typical transformants of each class, 

 both as donors and recipients in further transformations. 

 All proved to be stable on propagation in culture, but those 



Table I 



DiSSEMINATIVE TRANSFORMATION OF A RESISTANCE PROPERTY 

 NORMALLY INHERITABLE 



Standard sulfonamide resistance level (//g/ml.) of pneumococcal clones 



Progeny 



Donor 



a single-step 



mutant 



TiPSt- stage 

 transformants 



Second-stage 

 tpansfopmants 



10 



40 



10 



■* 40 



-*- 300 



600 



■*- 600 



Identified 

 genotypes 



120 



120 



120 



120 



which resembled the donor, Fn, gave the same multiple 

 classes of transformants, and the one having resistance to 

 800 (jLg./ml. also gave several transformants, when used as 

 donors. Certain other types seemed to transfer their geno- 

 types intact by transformation and accordingly were assigned 

 the unit marker designations Fa and Fd (or simply a and d), 

 as indicated in Table I. 



Starting from this basis, it was possible to seek and dis- 

 cover a third unit marker, b. By transforming one unit 

 strain with the DNA from another, it was possible to create 

 the paired combinations ab, bd, and ad, and from each of 

 these with the appropriate single marker DNA to prepare 



