Nuclearity amino acids

Spectrometric Analysis. Remarkable developments ia mass spectrometry (ms) and nuclear magnetic resonance methods (nmr), eg, secondary ion mass spectrometry (sims), plasma desorption (pd), thermospray (tsp), two or three dimensional nmr, high resolution nmr of soHds, give useful stmcture analysis information (131). Because nmr analysis of or N-labeled amino acids enables determiaation of amino acids without isolation from organic samples, and without destroyiag the sample, amino acid metaboHsm can be dynamically analy2ed (132). Proteia metaboHsm and biosynthesis of many important metaboUtes have been studied by this method. Preparative methods for labeled compounds have been reviewed (133). 

Numerous variations of this reaction have been studied, principally those involving a prior inclusion of the nuclear sulfur atom in a thioacylamino compound. Thus, thiobenz-amido acetaldehyde diethyl acetal (8) underwent ring closure to 2-phenylthiazole (9) on gentle heating (57JCS1556). Similarly, iV-thioacyl a-amino acids also undergo ready ring closure to thiazoles. 

Table 2 Raw Data and Posterior Modes from Dirichlet Mixtures for a Six Amino Acid Segment of Nuclear Hormone Receptors ...

Roberts, G. C. IC, and Jardetzky, O., 1970. Nuclear magnetic re.sonance. spectro.scopy of amino acids, peptides and proteins. Advances in Protein Chemistry 24 447-545. 

Sequence of amino acids that determine the transport of proteins into the nucleus. Although there is no clear consensus, nuclear localization signals tend to be rich in positively charged residues, which allow interaction with proteins from the nuclear import machinery (i.e., importins). 

Alternatively, one interesting drug delivery technique exploits the active transport of certain naturally-occurring and relatively small biomacromolecules across the cellular membrane. For instance, the nuclear transcription activator protein (Tat) from HIV type 1 (HlV-1) is a 101-amino acid protein that must interact with a 59-base RNA stem-loop structure, called the traus-activation region (Tar) at the 5 end of all nascent HlV-1 mRNA molecules, in order for the vims to replicate. HIV-Tat is actively transported across the cell membrane, and localizes to the nucleus [28]. It has been found that the arginine-rich Tar-binding region of the Tat protein, residues 49-57 (Tat+9 57), is primarily responsible for this translocation activity [29]. 

A comparison of several different steroid receptors with thyroid hormone receptors revealed a remarkable conservation of the amino acid sequence in certain regions, particularly in the DNA-binding domains. This led to the realization that receptors of the steroid or thyroid type are members of a large superfamily of nuclear receptors. Many related members of this family have no known ligand at present and thus are called orphan receptors. The nuclear receptor superfamily plays a critical role in the regulation of gene transcription by hormones, as described in Chapter 43. 

Despite the differences in nuclear structures between prokaryotes and eukaryotes, the genetic code, i.e. the combination of bases which does for a particular amino acid in the process of protein synthesis, is the same as it is in all living organisms. 

Although carotenogenesis in plants takes place in plastids, all of the carotenoid biosynthesis genes are nuclear encoded and their polypeptide products are imported into the plastids. Therefore, they contain a N-terminal transit peptide sequence. For example, the size of the transit peptide of PSY from ripe tomato fruit is approximately 9 kDa, corresponding to about 80 amino acid residues (Misawa et al, 1994). 

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