Transcriptional Maps of 10 Human Chromosomes at

:Sites of transcription of polyadenylated and nonpolyadenylated RNAs for 10 human chromosomes were mapped at 5–base pair resolution in eight cell lines. Unannotated, nonpolyadenylated transcripts comprise the major proportion of the transcriptional output of the human genome. Of all transcribed sequences, 19.4, 43.7, and 36.9% were observed to be polyadenylated, nonpolyadenylated, and bimorphic, respectively. Half of all transcribed sequences are found only in the nucleus and for the most part are unannotated. Overall, the transcribed portions of the human genome are predominantly composed of interlaced networks of both poly Aþ and poly A– annotated transcripts and unannotated transcripts of unknown function. This organization has important implications for interpreting genotype-phenotype associations, regulation of gene expression, and the definition of a gene. The current classification of protein-coding and noncoding genomic regions is based on intron-exon structures of well-characterized protein-coding genes. Noncoding genomic regions, which account for 98% to 99% of the human genome, consist of introns found within protein-coding transcripts and the intergenic re