Heterogeneous RNA

Figure 31-7 An abbreviated scheme of transcription, processing, and translation of mRNA,This complicated process involves excision of long intervening segments (introns) of heterogeneous RNA, with a stepwise reduction in length of the transcribed ribonucleic acid (RNA) to the 444 nucleotides (nt) of the final mRNA. The mRNA is capped at the S end and polyadenylated at the 3 end to stabilize it, then It is released into cytosol, where ribosomes read the code and assemble the globin chains.

It is known that protein synthesis is necessary for BR-induced effects in root tissue (25), and BR-treatment increases nucleic acid and protein synthesis in bean stem (26). In the pea stem segment, kinetic studies with selected protein and nucleic acid synthesis inhibitors showed no evidence for competitive inhibition in polypeptide chain elongation, post-transcriptional polyA addition to heterogeneous RNA, DNA-dependent RNA synthesis, or of the DNA-dependent RNA polymerase... 

The most prominent types of RNA are transfer RNA, ribosomal RNA, and messenger RNA. The structure and function of each of these molecules is discussed. Examples of other less abundant (but no less important) types of RNA (heterogeneous RNA and small nuclear RNA) are also described. 

Heterogeneous RNA (hnRNA) The primary RNA transcript of a gene, this usually refers to the unspliced precursor of mRNA. 

The information reviewed above has generally shown that 4 S (tRNA), rRNA, and heterogeneous RNA synthesis is detectable as early as the 4-cell stage in mouse embryos. It is further clear that the rate of incorporation of uridine into RNA increases steeply after the 8-cell stage and continues to rise throughout the development of the preimplan-... 

While the significance of these poly (A) sequences in mRNA is still unclear, the sequences can be considered as useful markers for detecting putative mRNA synthesis. As a result, heterogeneous RNA synthesized in rabbit embryos has been assayed for the presence of poly (A) containing RNA in an effort to provide evidence for, and an estimate of. 

Amount of Nuclear and Polysomal Heterogeneous RNA Associated WITH Poly(A) Sequences in the Preimplantation Rabbit Embryo... 

G9 Glazer, R. I., Nutter, R. C., Glass, L. E. and Menger, F. M. 2-Acetylaminofluorene and iV-hydroxy-2-acetylamino-fluorene inhibition of incorporation of orotic acid-5-[3H] into nuclear ribosomal and heterogeneous RNA in normal and regenerating liver. Cancer Res., 34, 2451-2458 (1974)... 

Bacterial and Mammalian Messenger RNA RNA Polymerase 118 Nuclear Heterogeneous RNA— A Precursor of Mammalian Messenger RNA 121 Visualization of Transcription 122... 

Several laboratories have measured the ability of hnRNA and mRNA to hybridize to frequently repeated DNA base sequences. The results clearly demonstrate that hnRNA contains more repetitive sequences than mRNA. When heterogeneous RNA is treated with ribonuclease, a ribonuclease-resistant core is obtained, much of which is made of polyadenyl-ic acid, the remaining double-stranded mixed sequences, and oligo U sequences. 

Heterogeneous RNA contains various regions resistant to RNase treatment one is the poly A sequence attached to the tail (see below), the others are various base sequences. The amount of RNase-resistant sequence varies considerably from species to species, and such portions of the hnRNA are referred to as... 

The poly A sequence hybridizes with poly T, and the portions have a sedimentation constant around 10 S. They are located at the 3 end of the hnRNA. The size of the poly A chain varies from one hnRNA molecule to another and usually ranges from 150-200 residues but some heterogeneous RNA contains no poly A chain. 

Figure 6. Idealized scheme of the mechanism of action of steroid and thyroid hormones using an intracellular binding protein or receptor. DNA, deoxyribonucleic acid RNA, ribonucleic acid Hn-RNA, heterogeneous RNA mRNA, messenger RNA.

Shemin, D., London, I. M., and Rittenberg, D. (1948). The in vitro synthesis of heme from glycine by the nucleated red blood cell. J. Biol. Chem. 173, 799-800. SoErao, R., Birnboim, H. C., and Darnell, J. E. (1966). Rapidly labeled HeLa cell nuclear RNA. II. Base composition and cellular localization of a heterogeneous RNA fraction. J. Mol. Biol. 19, 362-.3V2. 

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