Polynucleotide synthetases

E Polynucleotide synthetases Responsible for the linkage of two poly- or oligo-nudeotide moieties to form polynucleotide chains 6.5.1. Ligases forming phosphoric ester bonds... 

Transfer RNAs are small, single-stranded polynucleotides (70-90 bases long). The tRNA molecule is linked to its specific amino acid in a reaction that is catalysed by the enzyme tRNA-aminoacyl synthetase. It occurs in two stages ... 

These three compounds exert many similar effects in nucleotide metabolism of chicks and rats [167]. They cause an increase of the liver RNA content and of the nucleotide content of the acid-soluble fraction in chicks [168], as well as an increase in rate of turnover of these polynucleotide structures [169,170]. Further experiments in chicks indicate that orotic acid, vitamin B12 and methionine exert a certain action on the activity of liver deoxyribonuclease, but have no effect on ribonuclease. Their effect is believed to be on the biosynthetic process rather than on catabolism [171]. Both orotic acid and vitamin Bu increase the levels of dihydrofolate reductase (EC 1.5.1.4), formyltetrahydrofolate synthetase and serine hydroxymethyl transferase in the chicken liver when added in diet. It is believed that orotic acid may act directly on the enzymes involved in the synthesis and interconversion of one-carbon folic acid derivatives [172]. The protein incorporation of serine, but not of leucine or methionine, is increased in the presence of either orotic acid or vitamin B12 [173]. In addition, these two compounds also exert a similar effect on the increased formate incorporation into the RNA of liver cell fractions in chicks [174—176]. It is therefore postulated that there may be a common role of orotic acid and vitamin Bj2 at the level of the transcription process in m-RNA biosynthesis [174—176]. 

In addition to the reaction of mercaptopropionic acid, mixed anhydrides were also formed and identified starting from leucine and phenylalanine in the presence of Ca2+ ions, showing that RNAs can replace protein aminoa-cyl fRNA synthetase catalysts for amino acid activation. The formation of a detectable amount of aminoacyl S -phosphalc polynucleotide seems to be in contradiction with the instability predicted for aminoacyl adenylates (Table 1), however it can be explained by the low pH value increasing their stability and the fact that the selected RNA structures are likely to stabilize the mixed anhydride moiety of the covalent conjugate by favorable intramolecular interactions induced by folding. 

A second polynucleotide that has been studied extensively is ampligen, a mismatched poly rLpoly rC 12U resulting from mispairing of the duplex (16). This compound has been shown to induce interferon and to activate 2 -5 -adenosine synthetase (17). Ampligen has properties similar to those of poly rLpoly rC, although it has been reported to have broader activities and lower toxicities and is still in development. 

The formulas show the a-carbon and the side chain of the amino acid residues, line phosphatase, phosphorylase kinase, glycogen synthetase, troponin, RNA polymerase, polynucleotide, phosphorylase, and triglyceride lipase. Phosphoserine is also found in nonenzyme proteins which include histones, protamiens, ribosomal proteins, membrane proteins, ovalbumin, casein, and phosvitin often in substantial amounts. For example, there are 119 phosphoserines and only one phosphothreonine residue in phosvitin (72). 

Polymerases a collective term for enzymes that catalyse the formation of macromolecules from simple components, e.g. see separate entries for each of the following DNA-polymerase, RNA-polymerase, RNA-synthetase, RNA-dependent DNA-polymerase, Polynucleotide phosphorylase. Poly A-polymerase. 

Starter-dependent RNA synthetase. In vitro, polynucleotides can be synthesized by polymerization of S -nucleoside diphosphates with the release of phosphate. The process requires the presence of an oligonucleotide, which serves as a starter (primer). 

Other control mechanisms could influence srfA expression. As is the case with other peptide synthetase operons, there is a long untranslated region between the transcriptional start site of stfA and rhe first gene of the operon,. st/AA. Recently reported evidence suggests that this sequence and an RNA processing enzyme, Pnp (polynucleotide phosphorylase), function somehow to optimize the translation of srfA mRNA (129). 

Jones, GH. Guanosine pentaphosphate synthetase i from StrepiomYces iinitbnxicus is also a polynucleotide phosphoiylase. J Bacteriol 1996 (in press). 

Fro. 8. Diagrammatic representation of the relative mobilities on a MAK column of multiple species of E. coli Leu-tRNA at 0, 1, and 8 minutes after T2 phage infection. The responses of each peak (numbered 1 through 5) to tri- and polynucleotides are shown. The last two figures show the specificities of E. coli and yeast Leu-tRNA synthetase preparations for tRNA fractions at 8 minutes after infection. From T. Kano-Sueoka, M. Nirenberg, and N. Sueoka, J. Mol. Biol. 35, J (1968). 

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