The Structure of Genes

Structure. Unless DNA is transferred by a physical method, it is necessary to generate a structure able to carry the nucleic acid. When virus capsid or synthetic molecules are involved, they must be characterized physically to allow rational studies on how they ensure vectorization. The structures of gene transfer agents have to be defined to understand how they interact or associate with other... 

DNA matching. Studying the structure of genes and DNA, scientists can determine genetic relationships between different... 

The Structure of Genes.— What is known of the gene structure is summarized by using the most extensively studied genes as examples. 

The amount of sample required is quite small as little as 10 mole is typical So many peptides and proteins have been sequenced now that it is impossible to give an accurate count What was Nobel Prize winning work m 1958 is routine today Nor has the story ended Sequencing of nucleic acids has advanced so dramatically that it is possible to clone the gene that codes for a particular protein sequence its DNA and deduce the structure of the protein from the nucleotide sequence of the DNA We 11 have more to say about DNA sequencing m the next chapter... 

There are at least three different classes of crystallins. The a and (3 are heterogeneous assemblies of different subunits specified by different genes, whereas the gamma (y) crystallins are monomeric proteins with a polypeptide chain of around 170 amino acid residues. The structure of one such Y crystallin was determined in the laboratory of Tom Blundell in London to 1.9 A resolution. A picture of this molecule generated from a graphics display is shown in Figure 5.11. 

Weber, L, Steitz, T.A. The structure of a complex of catabo-lite gene activator protein and cyclic AMP refined at 2.S A resolution. /. Mol. Biol. 198 311-326, 1987. 

FIGURE 10.18 A model for the structure of the a-factor transport protein in the yeast plasma membrane. Gene duplication has yielded a protein with two identical halves, each half containing six transmembrane helical segments and an ATP-binding site. Like the yeast a-factor transporter, the multidrug transporter is postulated to have 12 transmembrane helices and 2 ATP-binding sites. 

Histone tails are the N-terminal regions of histones which reach outside the nucleosomes. They are not essential for the formation in of nucleosomes but are required for the formation of higher-order chromatin structures. The histone tails are also known to be heavily posttranslationally modified by acetylation, phosphorylation, methylation, etc. and are important for the regulation of gene activity. 

The structure of all TK receptors is similar in terms of expression oiTACR genes, since all these genes contain five exons intercalated by four introns [1, 5]. Exon I encodes for the N-terminal extracellular tail, the first intracellular (IC1) and extracellular (EC1) loops and the first, second, and third transmembrane domains (TM1, TM2, and TM3). Exon II encodes for the second intracellular (IC2) and extracellular (EC2) loops and the fourth transmembrane domain (TM4). Exon III encodes for the fifth transmembrane domain (TM5) and the third intracellular loop (IC3). Exon IV encodes for the sixth and seventh transmembrane domains (TM6 and TM7) and the third extracellular loop. Exon V encodes for the C-terminal intracellular tail only. A schematic drawing of the amino acid sequences and TK receptor organization is shown in Fig. 1. 

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