114 CHARLES A. III(iMA>. .IK. 



A. THK OUCANIZATION OK DNA l.\ lllK INTACT 1'HA(;K I'AKTICLES 



1. Stmlics on Purtldlh/ Oriented Pre p(iratie>n:^ 



If the DNA in the phage hi'ail were organized in a i^jjecial manner, 

 it would be likely that this would be revealed by a preferential align- 

 ment of regions of the molecule with respect to the long axis of the ])hage. 



When a concentrated suspension of anisometric particles is subjected 

 to a stress, the long axes of the particles are preferentially aligned in 

 the direction of the stress. It was l)y this technique that tobacco mosaic 

 virus (TMW) was first aligned (Bernal and Fankuchen. 1941). By 

 allowing a drop of concentrated T2 phage suspension to dry under 

 a cover slip on a microscope slide, Bendet, Goldstein, and Lauffer (1960) 

 fountl that there was a negative birefringence with respect to the direc- 

 tion of flow, while TM\' displayed a j:)Ositive birefringence in agreement 

 with the studies of others. Since the birefringence of TMV is known to 

 be positive (Franklin, 1955), while the birefringence of DNA is nega- 

 tive (Wilkins, Gosling, and Seeds, 1951), it was concluded that there is 

 a preferential alignment of DNA molecules in the direction of the long 

 axis of the phage particle. As the authors point out, there is a great 

 danger that DNA is ejected as a result of shearing the concentrated 

 suspension and certain precautions were taken to make this less likely. 



A more quantitative study of this same phenomenon was done by 

 Gellert (1961, 1962) employing flow-birefringence techniques. These ex- 

 periments revealed that the rotary diffusion constant, and hence the 

 fraction of particles that could be considered perfectly oriented at any 

 rate of shear, was essentially the same for intact phage particles and 

 for purified ghosts. The sign of the birefringence w^as exactly opposite: 

 positive for the ghosts, and negative for the intact phage (Fig. 1). By 

 subtracting these values, and knowing the fraction of particles that 

 could be considered perfectly aligned with the flow, Gellert concludes 

 that the phage DNA is so organized in the head that 10 to 15*^ of it 

 appears to be perfectly aligned with the long axis of the phage, if the 

 remainder is considered to be arranged at random. The form birefrin- 

 gence associated with the slightly anisometric cavity in which the DNA 

 resides would account for only a small fraction of this. Thus it appears 

 that there is an internal organization of the phage DNA. and this organ- 

 ization is reflected in the birefringence. 



In principle more detailed information can be had by X-ray diffrac- 

 tion studies on oriented phage preparations. Such a study was made by 

 North and Rich (1961). Their X-ray diffraction patterns show a high 

 degree of orientation, and a veiy strong reflection at 3.4 A which is 



