Polyribose phosphate

RNA has four kinds of bases along its polyribose-phosphate backbone and Tanaka assumes that only uracil is photochemically active, the other three bases being equivalently inert. In order to specify the statistical nature of the base sequence, the base composition and nearest neighbor frequencies are used, both of these being experimentally available quantities in many cases. If one assumes the sequence to be stationary, then ptt andpt, the probabilities that an arbitrarily given site is a uracil or an inert (photochemically) base, respectively, and the conditional probabilities, e.g., puu, suffice to represent the sequence. Because of the relations governing these probabilties, viz. 

A curious polyribose phosphate has been described in the squid Ommastrephes sloani (Maki, 1956) and this appears to have the same backbone structure as a ribonucleic acid, but without bases. Consequently it has only a marginal claim to inclusion here. 

How can the differences in specificity of the antibodies obtained from rabbit, mouse and hamster be explained Although the antibodies obtained from animals of the last two species have not as yet been well characterized, they have in common the cross-reaction with poly A poly U. As the purine and pyrimidine bases involved in these complexes are different, they probably recognize the double-helical structure. It is quite unhkely that the polyribose phosphate chain plays an exclusive role in this specificity since we have seen that the anti-poly I poly C antibodies of rabbit react better with poly dG poly dC than with poly rG poly rC. We cannot exclude the possibihty that poly I poly C complexed to MBS A undergoes modifications when it is introduced into the bloodstream. The discovery by Stern in 1970 of an enzyme which specifically hydrolyzes double-stranded RNA or poly I poly C, and which exists at different levels in the sera of nine mammaUan species illustrates this possibihty. There will thus exist in the antisera antibodies against the products of degradation, the quantity varying according to the species. 

Apparently this difference in reactivity of the various double-stranded complexes can be assigned to differences in their stereochemical structure orientation and distance of the bases in the interior of the double-helix, inclination of base pairs to the helix axis, and relative sizes of the large and small grooves, all of which characters can modify the external geometry of the polyribose phosphate chains. 

Antibodies with a strict specificity for triple-stranded structures do not react with either RNA or DNA. Since the bases are not readily accessible in a triple-stranded complex it is possible that the polyribose phosphate... 

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