244 ROBERT L. SINSHEIMER 



VI. Conclusion 



It is clear that the bacterial viruses include particles of a wide range 

 of size and morphological complexity, with a corresponding diversity of 

 biochemical, genetic, and radiobiological properties. Four major groups 

 of bacteriophage have been described: the T-even group plus T5, the Tl, 

 T3, plus T7 group, the temperate phages, and the minute phages, and 

 each group can be readily subdivided. 



Our knowledge of the biochemistry of infection and the associated ge- 

 netic and radiobiological phenomena is most advanced with respect to the 

 first group. Despite the complex nature of the T-even plus T5 group, as 

 it has been progressively revealed, it seems certain that much further 

 progress will be made with these phages toward the understanding of vi- 

 rus infection and the correlation of genetic and biochemical phenomena. 

 It must be said, however, that much of our knowledge of the biochemistry 

 of infection with this group of phages is concerned, for obvious reasons, 

 with the unique and highly specialized feature of the unusual pyrimidine 

 of the T-even phages. 



Since all of these groups are viruses, it seems plausible that there is 

 a basic sequence of biochemical events common to infection with all of 

 them. As yet knowledge of such a basic pattern is meager. Such problems 

 as the manner in which the invading DNA assumes direction of the cel- 

 lular metabolism, how it displaces the host DNA as the pattern for DNA 

 synthesis, and how it is preserved from degradation in those instances 

 in which the host DNA is extensively disrupted, are as yet quite obscure. 

 Add to these problems such special features as the manner of the creation 

 and preservation of the lysogenic state by the temperate phages, and the 

 manner of replication of the single-stranded DNA by the minute phage, 

 and it is clear that the bacterial virus systems still present remarkable 

 opportunities for biochemical exploration. The morphogenetic problems 

 implicit in the complex structure of such phage as the T-even group have 

 yet even to be approached on the molecular level. 



Considering the significance of the problems mentioned, it is apparent 

 that the study of the processes of bacterial virus infection offers a par- 

 ticularly favorable route to analysis of the most basic problems of cellular 

 and genetic biochemistry. 



