Genes encoding, cloning

The genes encoding the polypeptide backbones of a number of mucins derived from various tissues (eg, pancreas, small intestine, trachea and bronchi, stomach, and salivary glands) have been cloned and sequenced. These studies have revealed new information about the polypeptide backbones of mucins (size of tandem repeats, potential sites of N-glycosylation, etc) and ultimately should reveal aspects of their genetic control. Some important properties of mucins are summarized in Table 47-8. 

The genes encoding many glycosyltransferases have already been cloned, and others are under smdy. Cloning has revealed new information on both protein and gene stmcmres. The latter should also cast light on... 

An alternative approach is to synthesize an artificial gene in the test-tube starting with the appropriate deoxyribonucleotides. This approach, which demands that the entire amino acid sequence be known, has been used to clone genes encoding proteins 200 amino acids long. 

The oxidation of carotenes results in the formation of a diverse array of xanthophylls (Fig. 13.7). Zeaxanthin is synthesised from P-carotene by the hydroxylation of C-3 and C-3 of the P-rings via the mono-hydroxylated intermediate P-cryptoxanthin, a process requiring molecular oxygen in a mixed-function oxidase reaction. The gene encoding P-carotene hydroxylase (crtZ) has been cloned from a number of non-photosynthetic prokaryotes (reviewed by Armstrong, 1994) and from Arabidopsis (Sun et al, 1996). Zeaxanthin is converted to violaxanthin by zeaxanthin epoxidase which epoxidises both P-rings of zeaxanthin at the 5,6 positions (Fig. 13.7). The... 

LOTAN T and HIRSCHBERG J (1995) Cloning and expression in E. coli of the gene encoding 3-C-4-oxygenase, that converts (3-carotene to the ketocarotenoid canthaxanthin in Haematococcus pluvialis , FEBS Lett, 364, 125-8. 

Verdoes, J.C., Misawa, N., and van Ooyen, A.J., Cloning and characterization of the astaxanthin biosynthetic gene encoding phytoene desaturase of XanthophyUomyces dendrorhous [letter], Biotechnol. Bioeng. 63, 750, 1999. 

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