Abstract: The present invention relates to a method of RNA synthesis by RNA-dependent RNA polymerases (RdRp) displaying an RNA polymerase activity on single-stranded DNA templates and to a kit for carrying out the method. The RdRp showing DNA-dependent RNA polymerase activity has a “right hand conformation” and the amino acid sequence of said RdRp comprises a conserved arrangement of the following sequence motifs: a. XXDYS, b. GXPSG, c. YGDD, d. XXYGL, e. XXXXFLXRXX (with the following meanings: D: aspartate, Y: tyrosine, S: serine, G: glycine, P: proline, L: leucine, F: phenylalanine, R: arginine, X: any amino acid). This class of RdRp is exemplified by the RdRp enzymes of viruses of the Caliciviridae family. The present invention also relates to a method for transferring at least one ribonucleotide (rC, rA, rU or rG) to the 3?-end of a single-stranded DNA by using the RdRp of the invention.