(1973). Carbon Tetrachloride Hepatotoxicity: An Example of Lethal Cleavage. CRC Critical Reviews in Toxicology: Vol. 2, No. 3, pp. 263-297.

Carbon tetrachloride hepatotoxicity: an example of lethal cleavage

Requirement of an Escherichia coli 50 S ribosomal protein component for effective interaction of the ribosome with T and G factors and with guanosine triphosphate.

Pure initiation factor F3 dissociates 70S ribosomes into 30S and 50S subunits in a way which suggests that in vivo interaction with runoff ribosomes is responsible for their dissociation into subunits.

Activity of Initiation Factor F3 in Dissociating Escherichia coli Ribosomes

Homogeneous preparations of initiation factor F3 have both RNA binding and ribosome dissociation activities. But although DF activity could entirely account for the role of F3 in the ribosome cycle this factor has an additional function in formation of the initiation complex that may be related to its RNA binding properties.

Purification and Properties of Initiation Factor F3

Hydrolysis of Guanosine 5'-Triphosphate Associated with Binding of Aminoacyl Transfer Ribonucleic Acid to Ribosomes

The requirement of initiation factors F1 (highly purified) and F2 (electrophoretically homogeneous) for ribosomal binding of N-formylmethionyl transfer RNA (fMet ∼ tRNA) at low Mg2+ concentration (3.5 mM), with the trinucleoside diphosphate ApUpG as messenger, was studied under various experimental conditions with 30S + 50S ribosomes and with 30S subunits alone. The results were qualitatively the same in both cases but the amount of binding was two to three times higher when both 30S and 50S subunits were present. 

Although there was a virtually absolute requirement for F2 in all cases, considerable binding occurred at 0° in the absence of added F1. F1 addition stimulated binding up to twofold under these conditions. However, at 25°, the temperature at which the reaction is usually carried out, there was very little binding with F2 alone and addition of F1 stimulated the reaction five- to sixfold. 

Contrary to current belief, the GTP analog 5′-guanylyldiphosphonate (GMP-PCP) cannot replace GTP in the binding reaction. In particular, there was but little stimulation of binding (about 1.5-fold) by addition of F1 to F2-containing samples when GMP-PCP was used. In marked contrast, binding was stimulated up to sevenfold by addition of F1 when GTP was substituted for the analog. Under these conditions, there was an ApUpG and F1-dependent hydrolysis of GTP. This is observable with 30S subunits alone and can hardly be related to the occurrence of translocation. 

The results may be interpreted to mean that a complex relatively stable at 0°, but less stable at 25°, is formed upon addition of F2 alone. Conversion of the less stable to the more stable form of complex is made possible by addition of F1. This is accompanied or mediated by cleavage of GTP.

Polypeptide chain initiation in E. coli: studies on the function of initiation factor F1.

Previous work has shown that F2, one of several ribosomal factors involved in polypeptide chain initiation, functions in the binding of formylmethionyl-transfer RNA (fMet ∼ tRNAf) to a messenger RNA-ribosome complex. F2 was isolated from 1.0 M ammonium chloride washes of E. coli Q13 ribosomes as a protein homogeneous on polyacrylamide gel electrophoresis at both pH 4.5 and 7.8. Its molecular weight is approximately 80,000. Comparison of electrophoretic patterns of ribosomal proteins from NH4Cl-washed and unwashed ribosomes and F2, at pH 4.5, shows that F2 corresponds to the slowest-moving component of the proteins derived from unwashed ribosomes. This component is missing from the NH4Cl-washed ribosomes. The activity of F2 is stimulated by two additional factors, initiation factor F1 and a factor(s) present in a narrow ammonium sulfate fraction of the ribosomal NH4Cl wash. The nature of the latter is unknown.

https://www.pnas.org/content/pnas/62/4/1181.full.pdf

POLYPEPTIDE CHAIN INITIATION IN E. coli: ISOLATION OF HOMOGENEOUS INITIATION FACTOR F2 AND ITS RELATION TO RIBOSOMAL PROTEINS

The activity of the chain initiation factor F(2) in promoting the messenger-dependent binding of formylmethionyl-transfer RNA (fMet approximately tRNA(f)) to purified E. coli ribosomes is inhibited by sulfhydryl-binding reagents, such as N-ethylmaleimide or p-hydroxymercuribenzoate, but prior incubation with guanosine triphosphate (GTP) or with ribosomes largely prevents this inhibition. The effect of GTP suggests that it forms a complex with F(2) whereby "active" sulfhydryl groups become sheltered. Experiments on the time course of the binding reaction, with and without preincubation of F(2) with GTP, and gel filtration experiments with (3)H-labeled GTP lend support to this suggestion.

Yung-Bog Chae

Papers

Polypeptide chain initiation in E. coli: studies on the function of initiation factor F1.

POLYPEPTIDE CHAIN INITIATION IN E. coli: ISOLATION OF HOMOGENEOUS INITIATION FACTOR F2 AND ITS RELATION TO RIBOSOMAL PROTEINS

Polypeptide chain initiation in E. coli: sulfhydryl groups and the function of initiation factor F2.

Initiation of protein synthesis in Escherichia coli. I. Purification and properties of the initiation factors.