120 THE BIOSYNTHESIS OF PROTEINS 



eight nucleotides at most; but soluble RNA contain probably 10 times as 

 many. Such molecules seem too bulky to operate as adaptators in the sense 

 of Crick and it would seem that if soluble RNA is really an obligatory 

 intermediate on the pathway of protein synthesis, the template mechanism 

 must operate in a somewhat different way. 



It may be not necessary to assume that the template is at one time 

 covered with nucleotidic 'adaptors' each carrying its own amino acid; it is 

 conceivable that each specific soluble RNA adds in turn its amino acid to 

 the growing polypeptide. Such a process would of course be slower than the 

 other one. Protein synthesis takes several minutes in animal cells (Peters, 

 1957; Craddock and Dalgliesh, 1957; Loftfield and Eigner, 1958; Dintzis 

 et ah, 1958; Morris and Dickman, 1960), and only a few seconds in micro- 

 organisms (Boeye, 1957; McQuillen et ah, 1959; Cowie and McClure, 

 1958; Zalokar, in press). These are short times as compared to the usual 

 duration of biochemical experiments, but exceedingly long times in terms 

 of absolute rate of reaction. If it is assumed that soluble RNA and ribo- 

 somes must collide for the activated amino acids to be linked to the poly- 

 peptides, the collision frequency which can be estimated is sufficient to 

 support the observed rate of peptide bond synthesis, if more than one 

 collision out of ten thousand results in amino acid transfer (Ts'O and 

 Lubell, 1960). Sequential addition therefore does not seem excluded. It 

 would be compatible with many experimental data (Webster, 1959; Bishop 

 et al., 1960) including the apparent absence of intermediates in rapidly 

 synthesizing systems like living bacteria, and the non-uniform labelling in 

 extremely slow systems like homogenates of animal tissues. 



In a template process outlined by Dalgliesh (1953), several peptide 

 chains in different stages of development were attached simultaneously to 

 the templates, each by a small region as shown in Fig. 32. The polypeptides 

 all grow in the same direction by addition of activated amino acids, and peel 

 off behind the assembly zone. Future developments in molecular biology 

 will tell whether such a scheme is possible topologically. 



The experimental data available at present are not sufficient for a useful 

 discussion of a template process in terms of chemical reactions. But several 

 of the present lines of research might soon provide information relevant to 

 the template mechanism : further data on the relations between soluble and 

 ribosomal RNA, a better understanding of the function of amino acids in 

 RNA synthesis, further study on the function of peptide nucleotide com- 

 pounds will be very valuable. 



A metabolic relationship seems to exist between soluble and ribosomal 

 RNA, for energy-dependent transfers of oligonucleotides in both directions 

 have been demonstrated (Bosch et al., 1959). Hultin and von der Decken 

 (1959) and Moldave (1960) also observed a transfer of soluble RNA to the 

 microsomes and GTP seemed to promote the transfer. Clarification of these 



