Synthesis and Properties of Poly(s²C), a new Poly(C) Analog

Abstract

Polymerisation of 2-thiocytidine-5'-diphosphate (s2CDP) by polynucleotide phosphorylase from Escherichia coli leads to the formation of poly(s2C) which has been characterized by ultracentrifugation, enzymatic hydrolysis and phosphorolysis. The ultraviolet absorption derivative, optical rotatory dispersion and circular dichroism spectra of 2-thiocytidine and poly(s2C) have been measured. Evidence for n-nd* transitions in the absorption spectra of these compounds is derived from derivatives of ultraviolet absorption and circular dichroism spectra. The absorption-temperature profiles of poly(s2C) in the acid pH range prove the existence of double-stranded structures which are much less stable than those of poly(C). From these observations it is concluded that hydrogen bonding predominantly controls the stability of the poly(C) helix under acidic conditions. Poly(C), like poly(A), forms double-stranded structures in the acid pH range [I-31. Hydrogen bonding between bases and their cation and electrostatic interactions are thought to determine the stability of these helices. However, evidence was presented recently that charge-transfer interactions between cytosine and its cation in stacked structures might take place as well [4]. I n a variety of rare bases transfer RNA of Echerichia coli has been found to contain 2-thiocytosine [5]. The presence of a 2-thioketo group in cytosine should reduce the ability to undergo horizontal hydrogen bonding in helical structures, but a t the same time should intensify vertical interactions of the hydrophobic or electronic type. The properties of poly(s2C) as compared to those of poly(C) should indicate which factors contribute to the stability of the poly(C) helix under acidic conditions. The attempt was therefore made to synthesize poly(s2C) via the polymerisation of s2CDP by polynucleotide phosphorylase of E. coli.

A New Polynucleotide Complex Poly(s2C) · poly(I)

“…For a better understanding of the function of the rare nucleotide s2CMP in tRNA [2] knowledge of the behaviour of poly(s2C) under neutral conditions would be desirable. I n this paper we describe the interaction between poly(s2C) and poly (1) leading to the formation of the helical complex poly(s2C) -poly (1). Contrary to our original expectation, we find a stabilizing effect due to the presence of s2C in the helix.…”

“…The copolymer poly(C3,s2C) formed a helical structure in the acid pH range as revealed by a cooperative transition in the absorption temperature The reaction volume 1 ml contained 100 pmol Tris-HC1 pH 8.3, 2 pmol MgCl,, of 50 pmol Na,HPO,, 37.4 nmol poly(s2C) and 5 enzyme units polynucleotide phosphorylase. 0-0, Reaction mixture with the composition as described above but containing additionally 40 nmol poly (1). The change in absorbance a t 245 nm was monitored a t 20 "C profile.…”

The Effects of Thioketo Substitution upon Uracil‐Adenine Interactions in Polyribonucleotides

“…The conditions for the synthesis of po1y(s2U), poly(s4U) and poly(s2s4U) were already described in previous paper [20]. The S Z O ,~ values of the products were as follows: poly(s4U), 3.9 S; poly(s2U) 28 S; poly(s2s4U) 12.5 S.…”

“…The spectrophotometric equipment and methods employed in the following experiments have been described in previous papers [9,11,12]. The experimental details of sedimentation velocity analysis have also been reported elsewhere [9,12].…”

“…Although 4-thiouridine was found to exist in syn conformation [l] in the crystalline state no evidence was obtained from nuclear magnetic resonance, optical rotatory dispersion or circular dichroism Bpectroscopy that s4UMP residues in polynucleotides adapt syn conformation [2,3]. The s4UMP residues in polynucleotides were found to be the Abbreviations.…”