T4 RNA Ligase uses ATP to adenylate the 5'-end of a single-strand nucleic acid sequence. This activated adenylated-oligo is then covalently connected (ligated) to the 3'-OH of a second single-stranded sequence. Adenylated oligonucleotides containing a pyrophosphate linkage are substrates for T4 RNA Ligase in the absence of ATP (1). IDT will custom adenylate an oligonucleotide for use with RNA-Ligase using the chemical adenylation method of Unrau and Bartel (2). T4 RNA Ligase will use an adenylated DNA linker with similar efficiency as an adenylated RNA linker and IDT recommends use of adenylated DNA oligos for this application. Note that IDT requires blocking the 3'-end of an adenylated oligo so it cannot circularize; use of either 3'-Spacer C3 /3SpC3/ or dideoxycytosine /3ddC/ is preferred. References 1. England, T.E., Gumport, R.I. and Uhlenbeck, O.C. (1977) Dinucleoside pyrophosphate are substrates for T4-induced RNA ligase. Proc Natl Acad Sci U S A, 74, 4839-4842. 2. Unrau, P.J. and Bartel, D.P. (1998) RNA-catalysed nucleotide synthesis. Nature, 395, 260-263.