Any transcribed RNA molecule that is longer than 200 nucleotides and does not code for a protein. In mammalian cells such transcripts greatly outnumber those from protein-coding genes and their functions are often still unclear. They appear to regulate gene function through a variety of mechanisms. These include epigenetic silencing, by coating gene clusters to make them inaccessible to transcription machinery, as in X inactivation; blocking or recruitment of transcription factors; activation or trafficking of transcription factors; and post-transcriptional regulation of messenger RNA. Some may be precursors of small RNAs involved in RNA interference.