Consider the genome of the bacterium Mycoplasma capricolum, which causes several
ID: 91264 • Letter: C
Question
Consider the genome of the bacterium Mycoplasma capricolum, which causes several types of respiratory ailments in humans. There is a strong codon bias in this organism. Explain why this bias exists, and how is would be reflected in the translation of glutamic acid codons. For this amino acid this organism, draw the complete molecular structure of nucleotide positions #33, 34, 35, and 36 in the tRNA cognate for the codon that is used for this amino acid. Explain how the situation for glutamic acid codon and anticodon usage differs in Mycococcus luteus, Be very explicExplanation / Answer
Multiple competing factors have been proposed to bias the relative use of synonymous codons. Multiple factors such as UV radiation, nitrogen fixation and parasitism is responsible to explain GC variation in mycoplasma capricolumn resulting in differences in dietary nitrogen that cause concomitant differences in codon bias. codon bias variants include biased codon pairs and codon co-occurrence. Although translation initiation is the key step in protein synthesis, it is generally accepted that codon bias contributes to translation efficiency by tuning the elongation rate of the process. Moreover, codon bias plays an important role in controlling a multitude of cellular processes, ranging from differential protein production to protein folding. Analysis of the tRNA content of organisms in all domains of life showed that they never contain a full set of tRNAs with anticodons complementary to the 61 different codons; for example, In some Mycoplasma species and related species, the smallest sets are found, consisting of only 28 tRNAs with distinct anticodons. Translation of multiple synonymous codons by a single tRNA has been demonstrated to occur by wobble base-pairing: standard Watson-Crick base-pairing (A-U, G-C) is required at the first and second positions of a codon, and “wobbling” (e.g., G-U) is allowed at the third position of a codon (corresponding to the 5 position of the anticodon, i.e., position 34 of a tRNA). However, the affinity by which synonymous codons are recognized via wobble base-pairing is not similar. For instance, tRNAs with G in the 5 position of the anticodon have a higher binding affinity for C-ending codons than for U-ending codons. it can be suggested of greater translation efficiency by the translation apparatus (e.g., ribosomes) for certain codons over their synonyms.
Salmonella typhimurium in which the wobble nucleoside G34 had been replaced by an unmodified A in tRNAProGGG . The binding of the two mitochondrial tRNAArgACG, tRNAProAGG and tRNAThrAGU to codons CCC, CGC and ACC, respectively, would presumably require a wobble position A+34·C base pair.
Micrococcus luteus, a Gram-positive bacterium, is incapable of translating at least two codons. One of these unused codons was inserted in a gene to act as a nonsense site. An aminoacylated tRNA was synthesized which was complementary to this codon. The gene containing the missing codon was expressed in vitro in a M.luteus transcription/ translation system. Read-through of the missing codon occurred only when the complementary tRNA was included. The results demonstrate that M.luteus can be used for incorporation of amino acids via synthetically prepared aminoacylated tRNAs. The use of a M.luteus translation system provides a method for incorporation of non-natural amino acids which avoids the use of stop codons.