A procedure for amplification of minute amounts of an unknown RNA (or DNA) sequence. The RNA fragment is ligated at both ends to single-stranded palindromic oligodeoxynucleotide that provides a site for subsequent hybridization with a second oligodeoxynucleotide. Reverse transcription uses as a primer the hybridised oligodeoxynucleotide, and then PCR amplification generates a family of polynucleotides that can be treated with a restriction endonuclease to produce large fragments of the cloned RNA and smaller fragments of linker oligonucleotides.