Post-transcriptional modification

In addition to the role for the nucleosome-nucleosome interactions, the histone tails are known as the region that undergoes post-transcriptional modifications, such as acetylation, phosphorylation, and methylation (Fig. Ic) (Peterson and Laniel, 2004). These modifications trigger the formation of euchromatin (acetylation), heterochromatin (methylation), or metaphase chromosome (phosphorylation). The details of these modifications will be described in chapters 8-11. 

Moreover, overexpression of the same mutants inhibit DNA replication and block the cells at the Gl/S-phase transition (Kim et al, 2005), emphasizing the potential role of nucleolin mobilization. It is therefore highly probable that two different processes help the formation of RPA-nucleolin complexes after a genotoxic stress a post-transcriptional modification of nucleolin that renders the GAR domain of nucleolin accessible to RPA, and its p53-dependent relocalization to the nucleoplasm where a higher amount of RPA is available. Of importance, nucleolin relocalization is transient and lasts far less than replication inhibition (Daniely and Borowiec, 2000). This means that nucleolin-RPA interaction is only an initial event and that other mechanisms account for prolonged replication inhibition. 

Vitamin K is a component of the carboxylase enzyme that carboxylates the amino acid glutamate in proteins to form y-carboxyglutamate, which binds calcium ions i.e. it catalyses a post-transcriptional modification. Proteins so carboxylated include clotting factors (Factors 11, Vll, IX, and X) and two proteins in bone oesteocalcin (known as matrix-gln-protein) and bone gin protein (BGP). The... 

Puri, P.L. and Sartorelli, V. (2000) Regulation of muscle regulatory factors by DNA-binding, interacting proteins, and post-transcriptional modifications, /ourmil of Cellular Physiology, 185, 155-173. 

The tRNAs undergo post-transcriptional modification to produce specialized bases, such as pseudouridine, dehydrouridine, and methylcytosine. 

The structures of some modified nucleosides found in tRNA. The parent ribonucleosides are shown on the left in yellow screens. The other bases found in RNA result from post-transcriptional modification. 

Taniguchi, H. Hayashi, N. 1998. A liquid chromatography/electrospray mass spectrometric study on the post-transcriptional modification of tRNA. Nucleic Acids Res., 26,1481-1486. 

The eukaryotic transcript undergoes post-transcriptional modifications such as capping (5 -methyl-GTP cap) and 3 -polyadenylation (3 -poly A tail). 

Transgenicanimals Precise post-transcriptional modifications Easy to generate large amount of recombinant protein, e.g. one goat can generate 1 kg of recombinant protein in milk peryear Relatively inexpensive Risk of contamination with infectious agents Products can sometimes be unstable... 

BA is a potent differentiation agent in a wide variety of cancer cells in-vivo and in-vitro [23, 24]. Butyrate has been shown to specifically affect genes regulation by transcriptional and post transcriptional modifications. It induces dose dependent differentiation and inhibits proliferation of various malignant cells types including erythroleukemia, embryonal carcinoma and colon carcinoma [25, 26]. BA induced the expression of specific differentiation-associated genes when used at concentration between 0.5-10 mM. Differentiated cells are characterized by appearance of regulatory enzymes such as alkaline phosphatase [27]. 

In bacteria, which are prokaryotes, termination releases a mature mRNA for translation. In fact, because prokaryotes have no nuclear membrane separating the DNA from the cytoplasm, translation begins long before the mRNA is completed. In eukaryotes, transcription produces a primary transcript that must undergo extensive post-transcriptional modification before it is exported out of the nucleus for translation in the cytoplasm. 

Eukaryotic primary transcripts undergo three post-transcriptional modifications. These are the addition of a 5 cap structure and a 3 poly(A) tail, and RNA splicing. 

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