The activation of 50S and 30S E. coli ribosomes for polyphenylalanine synthesis

Interactions of guanosine triphosphate analogues with elongation factor G of Escherichia coli

Previous studies from this laboratory have shown that the GTP analogue guanosine 3'-diphosphate 5'-triphosphate (pppGpp) was almost without activity in the translocation reaction catalyzed by elongation factor G (EF-G), while it was fully active with elongation factor T (EF-T) and initiation factor 2 (IF-2). To assess the importance of the 3'-ribose hydroxyl itself in the translocation reaction, we examined polyphenylalamine synthesis and EF-G-dependent formation of N-acetylphenylalanylphenylalanylpuromycin (Ac-Phe2-puromycin) supported by 3'-deoxyguanosine 5'-triphosphate (3'dGTP) and 3'-deoxy-3'-aminoguanosine 5'-triphosphate (3'dNH2GTP). Like pppGpp, these nucleotides were similar to GTP in EF-T and IF-2dependent reactions. We also examined the ability of the dialcohol derived from GTP by periodate oxidation and borohydride reduction (rroGTP) and of ITP to support translocation. These compounds had shown significant, although reduced, activity with EF-T and IF-2. A spectrum of activity was found with these compounds in both poly(Phe) synthesis and Ac-Phe2-puromycin formation. All had significantly reduced activity relative to GTP, but all were significantly more active than pppGpp. A surprising finding was that the activities of all analogues relative to GTP were dependent on the reaction temperature in both poly(Phe) synthesis and Ac-Phe2-puromycin formation; these relative activities were significantly lower at 8 degrees C after than 37 degrees C. Furthermore, the extent of poly(Phe) synthesis with the analogues relative to GTP could be significantly affected by the amounts of EF-G and EF-T in the reaction mixture. Differences were minimized in the presence of rate-limiting EF-T and saturating EF-G and maximized in the presence of rate-limiting EF-G and saturating EF-T. This effect of reducing the level of EF-G in the reaction mixture thus mimicked the effect of lowering the incubation temperature, and a similar observation was made for Ac-Phe2-puromycin formation. GTP-supported formation of Ac-Phe2-puromycin at 8 degress C could be inhibited by 3'dNH2GTP, 3'dGTP, pppGpp, and ITP: these compounds were better inhibitors than they were substrates. Inhibition by other nucleotides was also noted. The GTP analogues were compared to GTP as substrates in EF-G-dependent reactions uncoupled from protein synthesis. Fusidic-acid-dependent binding of nucleotides to ribosomes and ribosome-dependent catalytic nucleotide hydrolysis were both examined, and the activity of the nucleotides as substrates in these ractions showed little correlation with their ability to support translocation.

Effects of polyamines and analogs on staphylococcal nuclease

The promoting activity of polyamine analogs (IV approximately XV) on staphylococcal nuclease with DNA as the substrate was compared with that of natural polyamines (I APPROXIMATELY III): I. NH2(CH2)3NH(CH2)4NH(CH2)3NH2(spermine); II. NH2(CH2)3NH(CH2)3NH(CH2)3NH2(thermine); III. NH2(CH2)4NH2 (putrescine); IV. CN(CH2)2NH(CH2)4NH(CH2)2CN; V. HOOC(CH2)2NH(CH2)4NH(CH2)2COOH; VI. C2H5OOC(CH2)2NH(CH2)4NH(CH2)2COOC2H5; VII. HO(CH2)3NH(CH2)4HH(CH2)3OH; VIII. CH3COHH(CH2)3NH(CH2)4NH(CH2)3NHCOCH3; IX. C2H5NH(CH2)3NH(CH2)4NH(CH2)3NHC2H5; X. NH2(CH2)3S(CH2)4S(CH2)3NH2; XI. NH2(CH2)3NH(CH2)2O(CH2)2NH(CH2)3NH2; XII. NH2(CH2)3NCH3(CH2)4HCH3(CH2)3NH2; XIII. CN(CH2)2NCH3(CH2)4NCH3(CH2)2CN; XIV. (CH3)2N(CH2)3NCH3(CH2)4NCH3(CH2)3N(CH3)2; XV. NH2(CH2)2O(CH2)2NH2 Replacement of the terminal groups by CN, COOH, COOEt, NHAc, NHEt, or N(CH3)2 remarkably decreased the activity. The compound VII with terminal hydroxyl groups had a lower promoting activity at low concentrations, but revealed higher activity at higher concentrations and, in contrast to spermine, no inhibition at all even at very high concentrations. Replacement of both internal amino groups by sulfur or NCH3 decreased the activity. The introduction of an ether bond into the internal methylene groups (compound XI) highly decreased the activity. Based upon these findings the possible relationship between structure and activity is discussed.

Kinetic evidence for the obligatory formation of a 30S initiation complex in polyphenylalanine synthesis initiated with N-acetylphenylalanyl-5RNA

The problem of whether the initiation of bacterial protein synthesis involves the obligatory formation of a 30S initiation complex intermediate was examined in a model system with N-acetylphenylalanyl-tRNA as initiator 5RNA nad poly(uridylic acid) as mRNA. The time courses of the formation of the 30S and 70S initiation complex with Escherichia coli ribosomes were measured simultaneously by stopping the reaction with dextran sulfate and differentiating the N-acetylphenylalanyl-tRNA bound to 30S ribosomal subunits from that bound to 70S ribosomes with RNase I, which hydrolyzes N-acetylphenylalanyl-tRNA bound to 30S subunits but not that bound to 70S ribosomes. A maximum in the 30S complex concentration was observed within the first 10-15 sec of the reaction, whereas 70S complex formed formed more slowly with a slight initial time lag. When an analog computer was programmed with rate constants determined separately for the formation of the 30S initiation complex from preformed 30S complex, kinetic curves very similar to the empirical curves were obtained for the entire time course of the reaction. The results show clearly that formation of the 70S complex obeys the kinetic laws for consecutive reactions, and the 30S complex is, therefore, an obligatory intermediate in the initiation of polyphenylalanine synthesis in the model system.

Requirement of initiation factor 3 in the initiation of polypeptide synthesis with N-acetylphenylalanyl-tRNA

Initiation factor 3 is required, along with initiation factors 1 and 2, for the incorporation of N-acetylphenylalanine into polypeptides and the formation of N-acetylphenylalanylpuromycin. Initiation factor 3 also strongly stimulates the binding of N-acetylphenylalanyl transfer RNA to isolated 30S ribosomal subunits. Phosphocellulose fractions of initiation factor 3 were found to catalyze N-acetylphenylalanine incorporation differentially with different synthetic messenger RNAs not containing any codons for N-formylmethionine. The results suggest that ribosomes recognize the initiator codon only through the initiator transfer RNA.

Polyamines and amino acid incorporation in vitro into microsomes of rat cerebral cortex

1. Polyamines were found to be associated with microsomes of rat cerebral cortex, the amount of spermine being about four times that of spermidine. Cell sap contained more spermidine than spermine. 2. Both polyamines were able to stimulate the incorporation of [(14)C]valine into microsomes in vitro with a maximum rate equal to 250% of the control. Polyamines stimulated at concentrations close to the amount of spermine and spermidine naturally present in the system. 3. Spermine (0.05mm) was used to study the mechanism of action of polyamines. The increasing of microsome and cell-sap concentration facilitated the action of spermine, but the same process was inhibited by increasing pH5-enzyme concentration. 4. Spermine did not affect the association of [(14)C]valine with tRNA in cell sap, but increased the rate of aminoacyl-tRNA formation in pH5 enzyme preparations. However, this process was not affected in any case when incorporating microsomes were present. 5. It is suggested that microsomes are the main site of action of polyamines.

[Regulation of nucleic acids synthesis by polyamines in germinating pollen of petunia]

Putrescine, spermine, spermidine, and agmatine in concentrations between 5-15 μg/ml inhibit pollen germination. Whereas spermine reduces pollen tube length, putrecine and agmatine do not affect pollen tube growth. Spermidine effects a small increase (about 5%) of pollen tube elongation. Spermine and spermidine can be found in pollen. Addition of spermine (7 or 10 μg/ml) depresses protein synthesis, whilst spermidine does not affect protein synthesis. On the basis of uridine-5-T incorporation it could be shown that both spermine and spermidine increase RNA synthesis. On tho basis of thymidine-T incorporation in the first hpurs of germination it seems that DNA synthesis is also stimulated by spermine and spermidine present in the medium. A net increase of nucleic acids was found when spermidine was added to the germination substrate.These results are interpreted as suggesting that, in the pollen tubes investigated, polyamine concentration may be a factor in the regulation of nucleic acid synthesis, resulting in a prolonged synthesis of specific proteins and in this way influencing growth and the developmental pattern of pollen tubes.