Genes — Nature and Consequent 



447 



a chemical capacity. The utilization of the 

 DNA template for DNA replication is, there- 

 fore, a relatively passive process with regard 

 to the DNA strand, and an active, chemical 

 one relative to the highly specific action 

 of DNA polymerase. If the DNA fiber 

 which serves as a template for DNA poly- 

 merase action is mostly a passive chemical, 

 it should be not at all surprising that DNA 

 serves as a template which is utilized by other 

 enzymes, provided that the raw materials col- 

 lected on the template are sufficiently similar 

 to deoxyribotides in physical and electrical 

 properties. This has, in fact, been found 

 true for polyribotides synthesized by RNA 

 polymerase which uses DNA as template. 

 Whether nucleotides other than those in DNA 

 and RNA, or still other substances, make 

 use of the DNA template in a similar or dif- 

 ferent manner has yet to be determined. Be 

 that as it may, it is suggested that the simplest 

 and broadest working hypothesis is that all 

 the functional characteristics of genes de- 

 pend upon the linear sequence of nucleotides 

 and the ways this can be used as template 

 by various substances and enzymes. In ac- 

 cordance with this view, serving as template 

 is the primary and only function of DNA. The 

 DNA template would have at least two uses 

 to which it is put, one involving the making 

 of DNA and another the making of RNA 

 polymers. 



We come then to a new definition of the 

 gene, as being any template whose use even- 

 tually results in self-replication of the tem- 

 plate, and which either retains this property 

 after mutation or is derived from a template 

 which can do so. We can still consider as 

 genetic any substance producing the same 

 phenotypic effects as a known gene. In 

 these terms, the RNA in plant viruses is 

 genetic material, just as is conserved chromo- 

 somal DNA. We do not know how viral 

 RNA functions in replication and self-repU- 

 cation, although there are several possibili- 

 ties. The host cell may contain a special 



RNA polymerase which uses the virus RNA 

 as template, the second replication being 

 virus RNA. Or, the virus RNA may be 

 used as template by a special host DNA poly- 

 merase, and the DNA chain produced might 

 then be used in a replication by regular RNA 

 polymerase which would produce virus RNA. 

 In either case, chemical and informational 

 self-replication would be a two-step process, 

 as is probably the case for DNA genes. 



Is chromosomal RNA genie? Only future 

 experimentation will provide the answer. 

 We need to know whether nuclear polymers 

 of RNA (synthesized using DNA as tem- 

 plate) can be used as template in a manner 

 suggested for virus RNA. If it is, it can 

 probably self-replicate some of its mutants. 



Because the DNA template contains par- 

 ticular nucleotides, each individual one has 

 meaning at least for the specification of other 

 complementary nucleotides (of DNA and 

 RNA type), and groups of these in some 

 cases eventually have purpose in the align- 

 ment of amino acids in polypeptides. It 

 should be recalled that some protein syn- 

 thesis apparently takes place in the nucleus. 

 Does this synthesis involve the use of the 

 RNA, or the DNA, or both, as template 

 material? In this connection it may be re- 

 marked that the hypothesis of nucleotide- 

 sharing translates into a phenomenon in 

 which a segment of DNA or RNA template is 

 utilized for two different purposes. Such 

 purposes may be to make more DNA (to be 

 conserved or not), more RNA (to be con- 

 served or not), or to order amino acids or 

 other substances. We need not specify 

 whether this template-sharing should occur 

 in the nucleus or the cytoplasm. 



We have already been successful in the 

 study of the replication and mutation of 

 DNA in vitro, dissociated from protein. 

 Recent studies ^ suggest that it may be pos- 

 sible also to study the enzyme-specifying 

 cistron in vitro. The one-to-one relation- 

 ^ Ey D. Novelli and coworkers. 



