128 Information Storage and Neural Control 



the viral RNA has become susceptible to added RNAse but is 

 still in large molecular weight form. It is these latter particles 

 which could be expected to function as units responsible for virus 

 replication. There is still a great excess of particles (about 10 fold) 

 in this state over the number of actual infectious units, a fact for 

 which an adequate explanation is lacking at present. 



The HeLa cell which is growing exponentially at the time of 

 poliovirus infection is drastically altered soon after infection. 

 Salzman et al. (37) have shown that net increases in protein, DNA 

 and RNA all cease upon infection. On the other hand, amino 

 acid incorporation continues after infection, but at a decreasing 

 rate (38), and incorporation of radioactive nucleic acid precursors 

 into RNA goes on at approximately the same rate but with a 

 different pattern. This changed pattern, however, is nonspecific 

 in the sense that halting growth by amino acid deprivation results 

 in the same change. 



It is important to remember in considering experiments of this 

 nature that a polio infected cell makes at most only .5 per cent of 

 its dry weight into virus and that these substantial amounts of 

 incorporation represent more RNA and protein than eventually 

 appear as virus material. Whether this indicates the formation 

 of new material under the direction of the virus or the turnover 

 of pre-existing cellular components is unknown. 



Late in the course of infection, cellular RNA is degraded and 

 lost into the medium as is a substantial amount of cellular protein 

 (37). This may represent a specific kind of loss. RNA is lost before 

 protein and both are lost prior to the liberation of virus into the 

 medium, a process which occurs as a burst and may be akin to 

 lysis of a bacterial cell after bacteriophage production (39, 40). 



Poliovirus is an extreme example of a virus with a destructive 

 action on its host cell. Other viruses have been shown to possess 

 lethal capacity for host cells without the almost complete destruc- 

 tion which is accompanied by virus release. Examples of this type 

 of interaction are found in adenovirus (41), herpes simplex (42), 

 and vaccinia (43) infections. All of these are held intracellularly 

 to the extent of about 90 per cent. In each of these cases the virus 

 apparently contains DNA. In adenovirus and herpes infections 

 there is stimulation of DNA synthesis to greater than normal 



