To study the mechanism of translation we have attempted to reconstruct the process from purified components. Protein synthesis was programmed by the RNAs of wild'type or amber mutants of bacteriophages f2 or MS2.Translation programmed by MS2 or f2am3 RNA does not occur using ribosomes, precharged aminoacyl-tRNAs, and the sum of the purified proteins involved in initiation (initiation factors; IF-i, IF-2, and IF-3), propagation (elongation factors; EF-Tu, EF-Ts, and EF-G) and termination (release factors; RF-1 or RF-2) of protein synthesis. Understanding of the mechanism by which the genetic code is deciphered depends on reconstruction of the translation process from purified components. A major step in accomplishing this task was achieved by Traub and Nomura (1) and Nierhaus (2) in the assembly of both the ribosomal subunits from rRNA and ribosomal proteins. Translation also requires the participation of 60 tRNAs, 20 activating enzymes, and proteins that promote initiation (initiation factors; IF-1, IF-2, IF-3), propagation (elongation factors; EF-Tu, EF-Ts, EF-G) and termination (release factors; RF-1, RF-2, RF-3) (3,4).In addition, several proteins have been reported to stimulate partial reactions of translation. One of these, EF-P, stimulates peptide-bond synthesis between fMet-tRNA and either analogues of aminoacyl-tRNAs, such as puromycin, or certain CCA amino acids (e.g., glycine or leucine) but not others (5-7). Protein X specifically stimulates synthesis programmed by certain synthetic templates other than poly(U) (8). According to one report, there is a factor that stimulates ejection of tRNAp ¶et from ribosomes (9). Finally, a series of activities has been described that is directly or indirectly implicated in the translation process. These include fMettRNA hydrolase (10), peptidyl-tRNA hydrolase (11,12), and the RR factor (13) that releases mRNA from ribosomes preventing reinitiation of translation (14). Study of conditionally lethal mutants defective in translation permitted identification of still another protein, "rescue," which acts in an undefined step of the ribosomal cycle (15-18).Reconstruction of translation from a DNA-directed system, ribosomes, and >30 proteins including several transcription factors, 20 activating enzymes, initiation, propagation, and termination factors revealed that the protein RR as well as activating enzymes, the transformylase, and several translation factors are essential for protein synthesis (3,(19)(20)(21). However, the requirements for several known and perhaps new components could not be scored, presumably because of the complexity of the system (20).To study the mechanism, it is essential to simplify the number of proteins required to catalyze protein synthesis. To do this, we have used a mixture of aminoacyl-tRNAs containing the labeled initiator tRNA and programmed each facet of synthesis with RNAs of either MS2, f2, or amber mutants of these bacteriophages. The bulk of the product synthesized by each of these bacteriophage mRNAs is the coat protein. ...

1. An acetyl-CoA--S-substituted cysteine N-acetyltransferase in rat liver and kidney preparations was investigated, by using an assay involving incubations with S-benzyl-L-cysteine and [l-14C]acetyl-CoA and extraction of the radioactive product with ethyl acetate. 2. The enzyme was associated with the microsomal fraction and could not be solubilized. Metal ions, EDTA and detergents did not significantly affect the enzyme activity. p-Chloromercuribenzoate and N-ethylmaleimide inhibited the enzyme. 3. Other S-substituted cysteines were acetylated at about the same rate as S-benzyl-L-cysteine. Acetylation of cysteine itself and of methionine, ethionine and tryptophan could be detected but was much slower. Acetylation of aspartic acid, glycine, phenylalanine and serine could not be detected. Palmitoyl-CoA was not a substrate. 4. The enzyme is presumably responsible for the acetylation step of mercapturic acid synthesis; a more physiological function is not yet known, except that the enzyme may be involved in acetylation of those amino acids which occur in elevated amounts in some disorders of amino acid metabolism.