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 A+ 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.

http://science.sciencemag.org/content/sci/308/5725/1149.full.pdf

Transcriptional maps of 10 human chromosomes at 5-nucleotide resolution

Polyadenylic acid [poly(A)] segments containing 150 to 250 nucleotides appear to be covalently linked to heterogeneous nuclear RNA (HnRNA) and messenger RNA (mRNA) in eucaryotic cells. The poly(A) is synthesized in the nucleus, and is probably linked initially to HnRNA that is ultimately transported as mRNA to the cytoplasm. Studies with inhibitors of RNA or poly(A) synthesis indicate that synthesis of poly(A) segments is independent of transcription. The poly(A) marker may prove useful to elucidate mRNA modification and transport in eucaryotic cells.s

https://science.sciencemag.org/content/sci/174/4008/507.full.pdf

Polyadenylic Acid Sequences: Role in Conversion of Nuclear RNA into Messenger RNA

The rapidly-labeled polyribosomal RNA component from mouse sarcoma 180 cells is retained on nitrocellulose (Millipore) membrane-filters at high ionic strength. This property is due to the presence of a polynucleotide sequence rich in adenylic acid that resists both T(1) and pancreatic RNase digestion. The resistant material shows sedimentation characteristics close to those of transfer RNA. The RNA molecules that contain this material can be separated from the rest of the polysomal RNA by differential phenol extraction with neutral and alkaline Tris buffers. Synthetic poly(A) exhibits the same behavior as the rapidly-labeled polysomal RNA with respect to Millipore binding and phenol fractionation. The characteristics of the rapidly-labeled polysomal RNA component permit its isolation free of ribosomal RNA.

A Polynucleotide Segment Rich in Adenylic Acid in the Rapidly-Labeled Polyribosomal RNA Component of Mouse Sarcoma 180 Ascites Cells

Polyadenylate sequences have been found covalently linked in heterogeneous DNA-like nuclear RNA of HeLa cells. This poly(A) material seems homogeneous in size and accounts for about 0.5% of such RNA. Similar poly(A) sequences were found in rapidly-labeled polyribosomal RNA, thought to be messenger RNA. A possible model for mRNA synthesis from large heterogeneous nuclear RNA precursor molecules is discussed.

https://www.pnas.org/content/pnas/68/6/1336.full.pdf

Polyadenylic Acid Sequences in the Heterogeneous Nuclear RNA and Rapidly-Labeled Polyribosomal RNA of HeLa Cells: Possible Evidence for a Precursor Relationship

This review concern recent experimental information areas of animal cell molecular biology which are relevant to the mechanism of gene regulation. New data regarding interspersion and clustering of repetitive sequence elements in DNA are considered Molecular characteristics of
animal structural genes and mRNAs are discussed, with particular reference the frequency of structural gene sequences, mRNA turn over and the interpretation of dipteran complementation groups. The molecular characteristics of nuclear RNAs, the primary transcription products, are reviewed. Evidence for transcription level regulation is summarized and the relation of nuclear
and mRNA examined. The protein activator branch of the Britten-Davidson model for gene regulation is further developed and considered in light of current knowledge.

/pdf/organization-transcription-and-regulation-in-the-animal-2eajr4e362.pdf

M G Caramela

Papers

The Isolation and Characterization of Adenosine Monophosphate-rich Polynucleotides Synthesized by Ehrlich Ascites Cells