478 J. BRACKET 



was collected and crystallized repeatedly, it was found that it had incor- 

 porated the labeled thiouracil in its PNA moiety only, apparently in the 

 form of thiouridylic acid. 



Other substances combining with nucleic acids or interfering with their 

 synthesis possess an inhibitory effect on the growth of plant viruses, e.g., 

 trypaflavine (Ryzhkov andSmirnova" and basic dyes (NickelP'^). Recently, 

 R. E. F. Matthews,'^ studying the effects of many analogues of the nucleic 

 acid bases on several plant viruses, found the guanine analogue, 5-amino- 

 7-hydroxy-l-ii-triazolo-(D)-pyrimidine (guanazolo) to be very effective in 

 the case of lucerne mosaic virus. Since inhibition due to guanazolo is re- 

 versed by adenine and guanine, it would appear that the compound acts 

 by blocking the incorporation of guanine into PNA; on the other hand, it 

 might well be that future work with isotopes will show, as in the case of 

 thiouracil, that guanazolo is incorporated as such in the PNA, perhaps 

 leading to the formation of an abnormal PNA and, consequently, to altered 

 virus particles with reduced synthetic abilities. 



3. Mechanism of Virus Multiplication 



For a further discussion of the mechanism of virus multiplication in re- 

 lation to protein synthesis, the reader should consult the recent analysis 

 made by Bawden and Pirie,^* whose main conclusion lies in "the idea that 

 the introduced virus attaches itself to a mechanism concerned with protein 

 synthesis in the host cell and affects it in such a way that thereafter one of 

 the products synthesized is virus." Thus virus multiplication would essen- 

 tially be a deviation from the normal mechanism of protein synthesis. As 

 Bawden and Pirie'^ point out, it is probably no coincidence that the small 

 plant viruses resemble the sites of protein synthesis in the cell as being rich 

 in PNA, as we shall see later. 



II. The Role of PNA in Morphogenesis 



This problem has been discussed at some length by the writer, both in a 

 book'^ and in a recent monograph^® in which more details will be found 

 than can be included in the present review. 



" V. L. Ryzhkov and V. A. Smirnova, Microbiology (U.S.S.R.) 17, 267 (1948); vide 



footnote 13. 

 '2 G. L. Nickell, Botan. Gaz. 112, 290 (1951). 

 13 R. E. F. Matthews, J. Gen. Microbiol. 8, 277 (1953). 

 '^ F. C. Bawden and N. W. Pirie, in "The Nature of Virus Multiplication" (Fildes 



and Van Heyningen, eds.), p. 21. Cambridge Univ. Press, New York, 1953. 

 '^ J. Brachet, "Chemical Embryology." Interscience, New York, 1950. 

 1* J. Brachet, "Le role des acides nucl^iques dans la vie de la cellule et de I'em- 



bryon." Masson, Paris, 1952. 



