Structural genes

Recombinant DNA techniques have provided tools for the rapid determination of DNA sequences and, by inference, the amino acid sequences of proteins from structural genes. The number of such sequences is now increasing almost exponentially, but by themselves these sequences tell little more about the biology of the system than a New York City telephone directory tells about the function and marvels of that city. 

All protein molecules are polymers built up from 20 different amino acids linked end-to-end by peptide bonds. The function of every protein molecule depends on its three-dimensional structure, which in turn is determined by its amino acid sequence, which in turn is determined by the nucleotide sequence of the structural gene. 

Figure 8.1 A region of DNA in the related bacteriophages lambda, 434, and P22 that controls the switch for synthesis of new phage particles. Two structural genes are involved in this switch one coding for a repressor protein and one coding for the Cro protein. Between these genes there is an operator region (OR) that contains three protein binding sites—ORl, OR2, and OR3.

Figure 9.1 The transcriptional elements of a eucaryotic structural gene extend over a large region of DNA. The regulatory sequences can be divided into three main regions (1) the basal promoter elements such as the TATA box, (2) the promoter proximal elements close to the initiation site, and (3) distal enhancer elements far from the initiation site.

Young, R. A., and Davis, R. W., 1983. Efficient isolation of genes using and-body probes. Proceedings of the National Academy of Sciences U.S.A. 80 1194-1198. Using andbodies to screen protein expression libraries to isolate the structural gene for a specific protein. 

Topoisomerase Type Structure Gene Predominant function in cell... 

Fig. 12. The nitrogen fixation genes of Azotobacter vinelandii. This orgEinism has three nitrogenase systems, viz nif, vnf, and anf, which it uses for fixing N2 under different environmental conditions. The boxes with slanted hatching indicate the structural genes of the three systems, those colored dark gray are required for eiU three systems, and those with vertical hatching are required for both the vnf and anf systems.

A preparation of the third nitrogenase from A. vinelandii, isolated from a molybdenum-tolerant strain but lacking the structural genes for the molybdenum and vanadium nitrogenases, was discovered to contain FeMoco 194). The 8 subunit encoded by anfG was identified in this preparation, which contained 24 Fe atoms and 1 Mo atom per mol. EPR spectroscopy and extraction of the cofactor identified it as FeMoco. The hybrid enzyme could reduce N2 to ammonia and reduced acetylene to ethylene and ethane. The rate of formation of ethane was nonlinear and the ethane ethylene ratio was strongly dependent on the ratio of nitrogenase components. 

Hemoglobin Illustrates the Effects of Single-Base Changes in Structural Genes... 

The structural genes of seventeen E-IIs and E-IIIs have been sequenced. In addition to the 15 listed in Table 1 of [5], the sequences of of R. capsulatus [6] and E-... 

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