Dg-Dc Tailing 
 
This procedure is used for cloning cDNA (complementary DNA) prepared from messenger RNA (1). Single-stranded cDNA prepared by reverse transcriptase is incubated with the enzyme terminal deoxyribonucleotide transferase and dCTP, which adds 5 to 10 C residues to the 3′ ends of the DNA molecules (C-tail). The second strands are synthesized with reverse transcriptase and oligo-dT as the primer, using the poly A tails of mRNA, and the double-stranded cDNA molecules are tailed with dC as before. The resulting molecules are cloned into vector molecules that have been tailed with poly G (about 10 bases per end) to create complementary ends to which the dC tails on the inserts hybridize. A recent modification is to use CTP instead of dCTP, which gives more uniform tails (2).
References
1. H. Land, M. Grez, H. Hauser, W. Linden Maier, and G. Scholtz (1981) Nucleic Acids Res. 9,  2251-2266.        
2. W.M. Schmidt and M.W. Mueller (1996) Nucleic Acids Res. 24, 1789–1791.