112 THE BIOSYNTHESIS OF PROTEINS 



tion is the nature and functions of the amino acid 'incorporation factors' 

 discovered by Gale, Disrupted Staphylococcus cells incorporate amino 

 acids readily under a variety of conditions (Gale and Folkes, 1955; Gale, 

 1955, 1957). Removal of the nucleic acids by salt extraction almost com- 

 pletely suppresses the incorporation. The process can be restored by the 

 addition of staphylococcal RNA or better of a ribonuclease digest of RNA. 

 The activity is not due to any nucleotide or oligonucleotide fragment of 

 the RNA as one would have anticipated. The activity is associated with 

 several substances present in minute amounts in such digests. A purified 

 preparation of the so-called 'glycine incorporation factor' promotes the 

 incorporation of glycine, phenylalanine, aspartic acid, leucine, glutamic 

 acid, arginine and lysine, and to a lesser extent that of valine, isoleucine, 

 tyrosine and proline (Gale, 1958). The same preparation also stimulates 

 the incorporation of adenine into nucleic acids (Gale and Folkes, 1958). 

 The chemical nature of these factors is completely unknown. The glycine 

 incorporation factor is reasonably stable to acid or alkali, it is devoid of 

 charge, except at high pH values, when it becomes slightly positively 

 charged. 



According to Wagle et al. (1960), the glycine incorporation factor 

 increases the (very low) incorporation which is observed in liver micro- 

 somes in the absence of the pH 5 fraction. The same laboratory has also 

 shown that a derivative of vitamin B12 stimulates very much amino acid 

 incorporation into the proteins of homogenates of liver from vitamin B12 

 deficient animals (Barker, 1958, 1959). The site of action of this substance 

 has not been located exactly, but it does not seem to concern the activation 

 steps (Mehta et «/., 1959 ; Wagle et «/., 1958 ; Szafranski et al, 1960) and the 

 observed effects might actually be indirect (Eraser and Holdsworth, 1959; 

 Arnstein and Simkin, 1959). Becarevic (1957) had also noted a restoration 

 by vitamin B12 of protein synthesis in ultraviolet-irradiated yeast. 



Yoshikawa and Maruo (1960) have isolated an amine which is strongly 

 bound to RNA preparations and which stimulates amylase formation by 

 B. subtilis. 



Many experimental facts remain to be explained and eventually inte- 

 grated into a scheme of amino acid incorporation. It is possible that the 

 presently accepted pathway involving activation enzymes, soluble RNA 

 and microsomes is only a first approximation to a more complex reality. 



D. THE SEQUENTIAL CONDENSATION OF AMINO 

 ACIDS INTO POLYPEPTIDES 



In the evolution of ideas on protein formation, two main working 

 hypotheses which were regarded as alternative and mutually exclusive 



