The Influence of Chain Length and Base Composition on the Specific Association of Oligoribonucleotides with Denatured

RNA made in Vitro on a DNA (from T2, T3, T4, or T7 phage) template was subjected to a limited digestion with ribonuclease T1 and fractionated according to chain length. The oligonucleotides of various chain lengths were annealed at various temperatures to denatured DNAs immobilized on membrane filters. In the absence of Mg++, a chain length of 10 or more ribonucleotides is required to form a ribonuclease-resistant complex with denatured DNA. In the presence of Mg++, oligonucleotides as small as octanucleotides can form a detectable complex with denatured DNA. The shortest oligonucleotides capable of forming a complex with denatured DNA do so with a high degree of specificity for species; oligonucleotides produced from T-even phage DNAs will form a complex only with T-even DNAs, not with T-odd DNAs, and vice versa. The expression of heterology between the T-even and T-odd phage DNAs seems to occur on passing from a chain length of 9 to 10. As expected, the temperatures for optimum complex formation and the melting temperatures of the oligoribonucleotidedenatured DNA complexes increase with the chain length of the oligonucleotides. When chain length is constant, these temperatures are considerably higher for the oligonucleotides produced from T-odd phage DNAs than for those produced from T-even ones, suggesting that the former oligonucleotides, having higher guanine + cytosine contents, form complexes that are considerably more stable than those formed by the latter.