Threonine codons

C. UCA is a codon for serine. It is converted to a termination codon by mutation A, to a proline codon by mutation B, to a threonine codon by mutation D, and to an alanine codon by mutation E. Only mutation C would produce no change in the protein, since UCU is also a codon for serine. 

Fig. 2-13. Change caused by nitrous acid in the threonine codon...

Another widely studied apo A-IV SNP is an A—>T polymorphism at nucleotide 2346 (first base of codon 347), which causes a threonine-to-serine substitution in the protein product.54-55 The A—>T variant at codon 347 occurs at almost double the frequency of the 360G—>T variant with a prevalence of 22% in Caucasian populations.55-56 However, ethnic differences have been described with lower frequencies in African blacks (9.5%) and Hispanic populations (12.9%).53 The 360G— T and 347A—>T genetic variants are in strong linkage disequilibrium and tend not to occur together.55-57... 

Smeda et al. (1993) reported that in a mutation of the psb A gene in a photoautotropic potato, atrazine resistance was attributable to a mutation from AGT (ser) to ACT (threonine) in codon 264 of the psb A gene that encodes the Qb protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates were detected compared to the unselected cells. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a Ser to Gly 264 alteration. Research has shown that triazine resistance by various algae and photosynthetic bacteria has been due to changes in many different binding sites (Oettmeier, 1999). 

The genes for all three deiodinases contain the TGA triplet in the coding region of the DNA, while the mRNA contains a UGA triplet at the corresponding position. Part of the coding sequence of type II deiodinase is shown in what follows. The entire protein consists of 266 amino acids. The codon resulting in selenocysteine is indicated by "SeC," where this amino acids resides in the context -glycine-serine-alanine-threonine-selenocysteine-proline-proline-phenylalanine-threonine- (Pallud et al., 1997) ... 

The codon CUA (CTA) encodes threonine and the codon AUA (ATA) methionine in mammalian mitochondria. 

The gene coding for TTR is on chromosome 18q. More than 50 genetic variants have been described, a few affecting hormone binding. The substitution of threonine for alanine at codon 109 increases the affinity of transthyretin for thyroxine and is associated with euthyroid hyperthyrox-inemia. Euthyroid hypothyroxinemia associated with genetic... 

Among the human tumor mutations identified by sequencing, 87.2% are single base substitutions and 12.8% are complex mutations and short deletions or insertions. Missense mutations have been observed at 231 of the 393 codons, including all the codons of the DNA-binding domain except codon 123. This codon (ATC, threonine) is well conserved in evolution, but experimental mutation (to Alanine) at this codon has been shown to activate, rather than suppress DNA-binding activity (Freeman et al., 1994). The vast majority of the mutated codons are recurrent mutation sites that are likely to result in dysfunctional p53. Silent mutations represent up to 3.9% of the mutations in the database and it is possible that mutations occurring at rare... 

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). 

Figure 15 Structureofms t A37 from the crystal structure of tRNA " (PDB ID 1XMQ)and theyW nucleoside from tRNA (PDB ID 1EHZ). The tricyclic ring of yW provides an extensive stacking interface for interaction with the cross-strand codon base. The carbamoyl threonine side chain of t A likewise is planar with the adenosine base, a conformation stabilized by a hydrogen bond from the amide to the N1 -nitrogen of A. This provides an extensive stacking interface as seen in the crystal structure of tRNA - bound to the 308 ribosome. ...

All organisms studied so far use the same genetic code, with some rare exceptions. One exception occurs in human mitochondrial mRNA, where UGA codes for tryptophan instead of serving as a stop codon, AUA codes for methionine instead of isoleucine, and CUA codes for threonine instead of leucine. 

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