Tyrosine codons

Sites at which nonsense mutations are detected are identified by their amber (A) or ochre (0) alleles (Coulondre and Miller, 1977). The 8 tyrosine codons in lacl each have two nonsense alleles, one amber and one ochre. The amber alleles at these sites are marked by the symbols and . 

Table III. BPDE-Induced Mutations at the Three TAC Tyrosine Codons...

Mu, D., Janes, S. M., Smith, A. J., Brown, D. E., Dooley, D. M., and Klinman, J. P., 1992, Tyrosine codon corresponds to TOPA quinone at the active site of copper amine oxidases, J. Biol. Chem. 267 7979n7982. 

In the genetic code of human nuclear DNA, one of the codons specifying the amino acid tyrosine is UAC. Another codon specifying this same amino acid is ... 

GotohN, Tojo A, Hino M et al. A highly conserved tyrosine residue at codon 845 within the kinase domain is not required for the transforming activity of human epidermal growth factor receptor. Biochem... 

Figure 28-10 Sequence of an E. coli tyrosine tRNA precursor drawn in a hypothetical secondary structure. Nucleotides found modified in the mature tRNA are indicated with their modifications (S4, 4-thiouridine Gm, 2 -0-methylgua-nosine 1°, N6-isopentenyladenosine jt, pseudouridine T, ribothymidine see also Fig. 5-33).241 A partial sequence of the tRNA gene past the CCA end is also shown. Note the region of local 2-fold rotational symmetry (indicated by the bars and the dot). The anticodon 3 -CUA (shaded) of this suppressor tRNA pairs with termination codon 5 -UAG.

But perhaps the discovery that caused the greatest surprise was the presence of these substituted adenine derivatives in the anti-codon loops of several transfer RNAs—not only in plant tRNAs but in those for serine and tyrosine in yeast (Bergquist and Matthews, 1962) in E. coli and probably in all other organisms. 

The option to remove the toxin from the environment of susceptible persons is taken in hemochromatosis, a common disorder of iron metabolism(101) that affects 1 in 300 persons of northern European descent. Most cases of hereditary hemochromatosis are attributed to a polymorphism of HFE, which results in substitution of tyrosine for cysteine at codon 282. The disease, untreated, causes liver cirrhosis, heart failure, diabetes and arthritis and leads to early death treatment by phlebotomy to remove excess iron allows affected persons to live a normal life span. 

In another study, proteins containing both mono- and diglycosylated amino acids, including glycosylated serine and tyrosine moieties, have been obtained by the suppression of nonsense codons in a cell-free expression system through the application of misacylated suppressor tRNAs activated with glycosylated serine and tyrosine derivatives (O Fig. 3) [32]. 

B. A nonsense mutation canses a prematnre stop codon on a single nncleotide substitution. The original seqnence, TAT, coding for a tyrosine, must have been mntated to either TAA or TAG, leaving a stop codon in place of the tyrosine. 

For hemoglobin Meoston the tyrosine would come from UAU and UAC codons while the normal hemoglobin s histidine is derived from CAU and CAC. Again we see the substitution of U for C (T for C in the parent DNA). Both are pyrimidines. U (T) usually forms 2 hydrogen bonding pairs while C forms 3. 

It follows that the array of codons represents the instructions for producing 20 amino acids, the so-called common amino acids. These amino acids are named and symbolized as alanine (Ala), arginine (Arg), asparagine (Asn), aspartate (Asp), cysteine (Cys), glutamine (Gin), glutamate (Glu), glycine (Gly), histamine (His), isoleucine (lie), leucine (Leu), lysine (Lys), methionine (Met), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), tryptophan (Trp), tyrosine (Tyr), and valine (Val). 

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