Nucleotidyl unit

The second difference concerns the conformation about the thymine-deoxyribose bond of dTTP, which in the ternary complex has the configuration corresponding to a nucleotidyl unit in the product, i.e. double helical DNA. This may represent an error-preventing mechanism 338 The RNA polymerases are more complex.339 They contain two Zn2+ per molecule, although additional zinc may bind at the Mg2+ site with inhibition. There may well be multiple roles for Zn2+, both structural and catalytic. The two sites in the enzyme from B. subtilis have different340 affinities for Zn2+, in accord with this proposition. The enzyme from E. coli has at least five subunits. Zn2+ is located on the subunit which binds DNA and on the subunit on which the initiation and elongation nucleotide binding sites are located.341... 

The second difference concerns the conformation about the thymine-deoxyribose bond of dTTP, which in the ternary complex has the configuration corresponding to a nucleotidyl unit in the product, i.e. double helical DNA. This may represent an error-preventii mechanism. ... 

CO-OPERATIVE CONFORMATIONAL PROPERTIES OF NUCLEOSIDES, NUCLEOTIDES AND NUCLEOTIDYL UNITS IN SOLUTION... 

The interrelation between conformational properties of nucleosides and nucleotides in solution is investigated, as far as possible, by plots of appropriate nmr parameters from results that are available in the literature. Only schematic representations of the plots are presented in this work so that the salient features can be discussed. The investigation provides methods by which results for nucleosides, mononucleotides and oligonucleotides can be rationalised. It is also shown that the conformational properties of adjacent bonds of nucleotidyl units are interdependent and analysis of the interrelationships provides insight into the cooperative nature of the conformational properties of nucleosides and nucleotides in solution. 

The interrelation between 0(5 )-C(5 ), euid C(5 )-C(4 ), bond conformations of nucleotidyl units has been investigated by plots of (= Jp5> + Jps OHz versus Hz which monitor the populations of the ( ) and conformers respectively. A schematic representation of the results shown in Figure 6 indicates that the behaviour of 5 -monoribonucleotides (anti-type, pyrimidine O, purine syn-type, pyrimidine A purine A) is markedly different from that of homo(py-pyQ, pu-pu ) and heterodimers (py-pu B, pu-py B ) Fcdnt lines connect results for molecules observed at different ten ratures. The dashed line is similar to that observed by Wood et al (1973) for syn- and anti-type 5 -mononucleotides and the slope (A /A 0.54) shows that the effect... 

The main difference between the results reported for conformations 1 to 4 and those reported under the heading A-RNA and B-DNA is that in the former case the calculated value includes the "neighbouring effect", that is the contribution to the computed shift of the other nucleotidyl unit of the dimer as weLL as the chemicaL shift variation due to the "rearrangement effect" (that means the A6 due to the conformational difference between the isolated mononucLeotide taken as reference and the corresponding nucleotidyl unit in the dimer), while in the second case, only the "neighbouring effect" is taken into account. 

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