Fragments of noncoding RNA in plasma of human blood

Mammalian extracellular fluids, such as plasma of blood or plasma of milk, contain cell-free RNAs. Fragments of ubiquitously expressed mRNAs as well as tumor-specific and viral RNAs have been previously revealed in human plasmas by template-defined RT-PCR. In the present work we aimed to detect major forms of human blood plasma RNAs or to reveal new forms by using two approaches which were independent of context of RNA templates. The first approach was based on ligation of total plasma RNAs with adapter-oligoribonucleotides, reverse transcription of RNA-constructs, and amplification and cloning of cDNA. The second EST-like approach involved reverse transcription of RNAs with 3'-N6 degenerate primer, ligation of cDNA with dsDNA-adapter, amplification and cloning. Using these approaches we determined tens of tiny RNAs of human plasma and identified several long (>100 nt) RNAs. Most of tiny RNAs could be attributed to the fragments of rRNAs, whereas longer forms are representatives of noncoding RNAs.