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

Abstract

Poly(s2C) -poly(1) complex formation (where s2C = 2-thiocytidylate) was shown by spectrophotometric titration, absorption-difference spectroscopy and hydroxyl-ion titration. The absorption temperature profile of the complex does not display a transition between 10 and 100 "C. Cooperative melting with a transition midpoint at 77 "C was observed only after destabilisation by 30°/, ethyleneglycol. A stabilizing effect of s2CMP residues in helices is further shown by the observation that 2501, sWMP in poly(C,,s2C) * poly(1) significantly increased the thermal stability compared to poly(C) * poly(1). The ultraviolet absorption spectrum, first derivative absorption spectrum and circular dichroism spectrum suggest a weak n-n* transition at 320 nm in poly(s2C) * poly(1). Unlike other nucleoside diphosphates the polymerisation of s2CDP by polynucleotide phosphorylase from Escherichia coli occurred with it pronounced lag phase which disappeared after the addition of oligonucleotide primers.Recently we reported the enzymatic synthesis of a new poly(C) analog, poly(s2C) [l]. Poly(s2C) like poly(C) forms a helical structure a t acidic p H which is, however, much less stable than a poly(C) helix under corresponding conditions. We assumed that the low stability of the poly (s2C)helix in the acid pH range is the consequence of N-H . . . S hydrogen bonding. 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. I n fact we found it necessary to extend our studies to copolymers of CMP and s2CMP to demonstrate the differences in the properties of CMP and s2CMP due to the introduction of the 2-thioketo group. Polymers with s2CMP only were so stable we could not detect helix-coil ~~ Abbreviations. sZCyd, 2-thiocytidine ; sZCMP, 2-thiocytidine-5'-phosphate ; s2CDP, 2-thiocytidine-(i'-diphosphate poly(s2C), poly-2-thiocytidylic acid; poly(C,,s2C), random copolymer of average composition CMP : s2CMP = 3 : 1 ; these and other abbreviations for nucleatides and polynucleotides follow CBN rules, see Eur. J . Biochenz. 15, (1970) 203. A,,, unit, amount of material which in 1 ml of solution gives an absorbance of 1 a t 250nm when measured in a cell of 1-cm path length. CD, circular dichroism.

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

“…The polarizable thioketo-groups of s~UMP, s2UMP or s2s4UMP will certainly effectively participate in dipole-induced dipole interactions if they are in appropriate positions. Recently we reported the physical properties of a new polynucleotide complex poly(s2C) -poly(1) [12]. The vertical interactions of sequent 2-thiocytosine bases stabilize the complex to such a degree, that its thermal denaturation in the absence of organic solvents cannot be achieved.…”

“…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].…”

“…The experimental details of sedimentation velocity analysis have also been reported elsewhere [9,12]. …”

Induction of interferon by polyribonucleotides containing thiopyrimidines

“…According to specifications given, s20,w values were 10-15; 8-13; >10; 'v10 and >8 S, respectively. Poly(I).poly(s C) was prepared by spectrophotometric titration (3). A single lot with s = 20,w 14.1 was used for all animal experiments.…”

Stacking patterns of thiopyrimidines: the crystal structure of 2-thiocytosine picrate

“…The ability of thiopyrimidine residues to stabilize the secondary structure of polynucleotides has been attributed to enhanced base-stacking interactions induced by the sulfur substituents (Faerber, Scheit & Sommer, 1972;Scheit & Gaertner, 1969;Bahr, Faerber & Scheit, 1973). Recent reviews have suggested that the bases in crystal structures of thiopyrimidines generally exhibit characteristic stacking patterns that involve intimate contacts between the sulfur substituent of one base and the ring systems of neighboring bases (Saenger, 1973;Saenger & Suck, 1973).…”