Protein specifiers

Most reactions in cells are carried out by enzymes [1], In many instances the rates of enzyme-catalysed reactions are enhanced by a factor of a million. A significantly large fraction of all known enzymes are proteins which are made from twenty naturally occurring amino acids. The amino acids are linked by peptide bonds to fonn polypeptide chains. The primary sequence of a protein specifies the linear order in which the amino acids are linked. To carry out the catalytic activity the linear sequence has to fold to a well defined tliree-dimensional (3D) stmcture. In cells only a relatively small fraction of proteins require assistance from chaperones (helper proteins) [2]. Even in the complicated cellular environment most proteins fold spontaneously upon synthesis. The detennination of the 3D folded stmcture from the one-dimensional primary sequence is the most popular protein folding problem. 

Evans, T., Rosenthal, E. T Youngblom, J., Distel, D., and Hunt, T. (1983). Cyclin a protein specified by maternal mRNA in sea urchin eggs that is destroyed at each cleavage division. Cell 33 389-396. 

Amino acids are joined together in a specific order determined by tRNAs, ribosomes, and associated enzymes that translate the mRNA. Each amino acid is joined to its neighbor by a peptide bond. The specific amino acid sequence of a protein specifies its three-dimensional structure. Some proteins require the help of chaperonins to fold into a functional configuration. When synthesis of a polypeptide chain is completed on a ribosome, it is released from the ribosome and may join with one or more similar or different polypeptides to constitute a functional protein. 

How does the amino acid sequence of a protein specify its three-dimensional structure How does an unfolded polypeptide chain acquire the form of the native protein These fundamental questions in biochemistry can be approached by first asking a simpler one What determines whether a particular sequence in a protein forms an a helix, a (3 strand, or a turn One source of insight is to examine the frequency of occurrence of particular amino acid residues in these secondary structures (Table 2.3). Residues such as alanine, glutamate, and leucine tend to be present in a helices, whereas valine and isoleucine tend to be present in (3 strands. Glycine, asparagine, and proline have a propensity for being present in turns. 

The sequence GAGGU is complementary to a sequence of five bases at the 3 end of 16S rRNA and is located several bases upstream of an AUG start codon. Hence, this region is a start signal for protein synthesis. The replacement of G by A would be expected to weaken the interaction of this mRNA with the 16S rRN A and thereby diminish its effectiveness as an initiation signal. In fact, this mutation results in a 10-fold decrease in the rate of synthesis of the protein specified by this... 

Transcriptional Control by Maternally Derived Bicoid Protein Specifies the Embryo s Anterior... 

It is noteworthy that in the eye lens of the duck, gene duplication and separation of function may have occurred with one gene product acting primarily as a 6-crystallin and one acting primarily as an argininosucccinate lyase, although the two proteins specified by the respective cDNA clones are 94% identical in predicted amino acid sequence [186]. 

Shivakumar, A. G., Hahn, J., Grandi, G., Kozlov, Y., and Dubnau, D, (1980). Posttranscriptional regulation of an erythromycin resistance protein specified by plasmid pE194. Proc. Natl. Acad. Sci. USA 7,3903-3907. 

Ribonucieic acid (tobacco done, iambda.5A gene RB7 protein-specifying 1524-nucieotide messenger) 790c, 3126a, 4249... 

Ribonucleic acid (tobacco clone. lambda.5A gene RB7 protein-specifying 1524-nucleotide messenger)... 

Many genes are present in the genotype in several copies, and these copies are often different from one another. This is because the protein specified by any one gene copy has unique physical and chemical properties of its own. Itfunctions most efficiently at a certain temperature, pH and salt concentration. If an important protein is represented in several different gene versions, a broad band rather than a narrow range of temperatures and chemical conditions will be optimal. 

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