The Periodicity in Tobacco Mosaic Virus 



261 



Fig. 3. TMV degraded in alkaline solution and outlined by 

 same solution. Magnification 140,000. 



Fig. 4. TMV stained with 40 ',',', phosphotungstic acid, and 

 thoroughly washed before allowed to dry. Magnification 

 X 140.000. 



to be deposited around the surface of the particle, and 

 if the particle has an inner surface which is accessible 

 to salt, the salt will be deposited there too. The 

 diameter of the core appears to be about 20-30 A 

 in the E M, which is in agreement with the x-ray 

 values. 



These outlined particles show one or two other 

 features of interest, whose significance is unevaluated. 

 They do not seem to show any obvious external 

 grooving of the particle, and the short lengths of 

 degraded virus do not seem to be showing any 

 material protruding beyond the ends of the particle. 

 Degradation always seems to take place by almost 

 accurately transverse cleavage. 



The "outlining" technique would appear to be 



quite a useful one for this type of specimen, particu- 

 larly as it is so simple and gives excellent contrast 

 and resolution. 



J am indebted to Dr. J. D. Watson and Dr. R. Franklin 

 for interesting me in this material. 



References 



1. Bernal, J. D. and Fankuchen, I., /. Gen. Physiol. 25, 



111 (1941). 



2. Franklin, R. E., Nature 175, 379 (1955). 



3. Franklin, R. E. and Klug, A., Biochini. Biophys. Acta 



19, 403 (1956). 



4. Hall, C. E., /. Biophys. Biochem. Cytol. 1, 1 (1955). 



5. Schramm, G., Schumacher, G., and Zillig, W., Z. 



Natiirforsch. 10, 481 (1955). 



6. V/atson, J. D., Biochini. Biophys. Ada. 13, 10 (1954). 



Electron Microscope Studies on the Periodicity in Tobacco 



Mosaic Virus 



R. E. F. Matthews, R. W. Horne and E. M. Green 



Moltciio Iiulitiac, Cambridge, ami Cavendish Laboratory, Cambridge 



Investigations by x-rays on the study of the sub- 

 unit structure of tobacco mosaic virus (1, 3, 4, 5, 8) 

 have suggested that such a structure is arranged in 

 the form of a helix with a pitch of 23 A and a repeat 

 distance of 69 A. This paper is concerned with an 

 attempt to resolve such small surface detail on the 

 surface of tobacco mosaic virus rods using a single 

 stage carbon replica technique (2). 



Pre shadowed replicas applied to the study of crystal 

 virus structures (6) indicated that small biological struc- 

 tures could be resolved employing this technique. The 

 work described here was carried out on purified suspen- 

 sions of TMV dried down on carefully cleaned glass 



surfaces and carbon evaporated onto the preparation at 

 an angle of about 30 from the horizontal. The carbon 

 replica is then stripped from the glass surface and placed 

 in 2 A' KOH at 60 C for approximately 20 minutes to 

 remove any remaining rods attached to the replica. After 

 a final washing the replicas were examined in the electron 

 microscope at instrumental mangifications of ■' 40.000 

 and 80.000. 



Preshadowed replicas have pro\cd to be of little \alue 

 as much of the structure is obscured by the deposited 

 metal tending to confuse rather than reveal much of the 

 fine structure. 



Three features have been resolved: (a) a structure 

 repeating along the rod axis spaced at 46 A in the 



