Hypothetical phylogenetic sequence

Figure 12. Hypothetical phylogenetic sequence of hopanoids giving rise to sterols. X-ray crystallographs obtained by Dr. Jane Griffin and coworkers of the Medical Foundation of Buffalo. (1 Tetrahymanol, 2 Isoarborinol, 3 Cycloartenol, 4 Lanosterol, 5 Sitosterol, 6 Cholesterol)...

Figure 1. An unrooted phylogenetic tree of the myosins based on the amino acid sequence comparison of their head domains demonstrating the division of the myosin superfamily into nine classes. The lengths of the branches are proportional to the percent of amino acid sequence divergence and a calibration bar for 5% sequence divergence is shovk n. The different classes of myosins have been numbered using Roman numerals in rough order of their discovery and hypothetical models of the different myosin structures are shown. Question marks indicate either hypothetical or unknown structural features, and only a fraction of the known myosins are shown. (Taken, in modified form, from Cheney et al., 1993).

A phylogenetic tree constructed by Hood and Talmage (7) from the first 20 N-terminal residues of 41 human k and 23 X proteins is shown in Fig. 12.4. Note that certain symbols, such as kI-III, represent hypothetical precursor molecules. (The actual structure of the precursor is predicted by the method.) The KL symbol in the figure is the hypothetical common precursor from which k and X chains are derived. The mutational distances shown on the tree would of course be much greater if the entire sequences were known and charted. More elaborate trees were subsequently constructed, on the basis of additional sequence data, by Smith et al., who also present phylogenetic trees for mouse and human Vh regions (8). 

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