THE GENE AND BIOCHEMISTRY 



gested it. We are only now beginning to do something definite about 

 it from an experimental standpoint. Since the specificities of enzymes 

 are referable to protein specificities, the hypothesis implies that genes 

 direct protein specificities. In this case we might expect that the 

 specificities of proteins other than those found in enzymes would show 

 a direct relation to genes. This is indeed the situation as evidenced 

 by the fact that in many organisms a general one-to-one relation be- 

 tween genes and antigens has been shown (22,47). It is true that a 

 few deviations from this correspondence are known, but they may well 

 represent instances in which antigens have specificities made up of two 

 components, each corresponding to one gene. 



If we knew the chemical nature of genes, we should be in a 

 much better position than we are now to determine how they direct 

 protein specificities. Direct chemical analyses of whole chromosomes 

 show them to be largely nucleoprotein (27), which suggests that genes 

 too are nucleoproteins. But since chromosomes probably contain 

 much nongenic material, the deduction is not too satisfying. Ultra- 

 violet radiation induces gene mutation; and its efficiency in this re- 

 spect varies with wave length in the same way as does its absorption 

 by nucleic acid (20,45), strongly indicating that the energy eff'ective 

 in producing mutations in genes is absorbed by nucleic acid. The 

 simplest assumption possible is that this is so because the nucleic acid 

 is part of the gene. 



The similarity of genes and viru.ses constitutes a third line of evi- 

 dence concerning the chemical nature of genes. Both have the property 

 of self-duplication, which in both cases is dependent on the presence of 

 a series of compounds such as those found in the living cell. Genes 

 and viruses appear to be within the same size range (46). Both are 

 capable of undergoing mutation to new forms which have altered 

 biological activities but retain the power of self-duplication (46). 

 Since viruses and genes have so many properties in common, it is 

 probable that they are similar in chemical makeup. Following 

 Stanley's isolation of crystalline tobacco mosaic virus, several other 

 viruses have been prepared in pure form and all have been shown to 

 be nucleoproteins (5,12,46). The circumstantial evidence that genes, 

 too, are nucleoproteins, or at least contain nucleoproteins as essential 

 parts, is therefore substantial. 



In duplicating themselves, genes have been assumed to act as 



