4 CONTROL MECHANISMS IN CELLULAR PROCESSES 



It is clear that a number of different tvpes of gene control over 

 enzyme formation and function exist. Mutations do cause qualita- 

 tive changes in specific enzyme proteins. However, genetic effects 

 on the quantitative aspects of enzyme formation are also observed. 

 Enzyme levels in the cell and the time and rate of appearance of en- 

 zymes are often affected by gene change. In addition environmental 

 factors come into play in interactions with the genome in the regula- 

 tion of enzyme formation (Bonner, 1959; Bonner et al., 1960). Some 

 of these manifestations of gene control will be discussed bv other 

 participants in the symposium (Vogel, 1961). Furthermore, there 

 is evidence for both intergenic and intragenic interaction at the 

 enzyme level as seen in studies on suppressor gene action, partial 

 reversion, and complementation (Fincham, 1959; Yanofsky and St. 

 Lawrence, 1960). 



From the studies with many gene-enzyme systems in diverse 

 organisms, and particularly from current investigations with human 

 hemoglobins (Ingram, 1958; Singer and Itano, 1959), a concept of 

 the relationship between gene and protein has emerged which is 

 providing a working basis for future explorations in molecular ge- 

 netics. As a result of studies on DNA transformations in bacteria, 

 on the biochemistry of phage infection and replication, and on the 

 physical, chemical, and enzymatic studies of DNA structure, a model 

 of the genetic material as a replicating complementary two-stranded 

 structure has evolved (Crick, 1958). This structure is thought to 

 contain, in its specific nucleotide sequence, the coded information 

 corresponding to the amino acid sequences of specific proteins. A 

 gene, then, defined in these terms, is a polynucleotide segment which 

 controls the primary structure of a protein. This certainlv does not 

 exclude the possibilitv that genetic information also specifies sec- 

 ondary and tertiary structure. 



On the basis of the limited experimental evidence available and 

 considerable theory, the current interpretation of the role of the gene 

 in protein synthesis can be summarized as follows: Base-coded in- 

 formation in DNA is transferred to RNA which participates with 

 ribosomal or microsomal components in the determination of the 

 primary structure of specific protein ( Hoagland et al., 1959 ) . Amino 

 acids are enzymatically activated and transferred to specific soluble 

 RNAs. These amino acid-RNA complexes then enter the ribosomes 

 and are oriented in or on the ribosomes in a sequence specific for a 

 particular protein, thereby reflecting the "information" originallv 



