Small gene families

Plant apocarotenoids have a wide variety of structures and functions. As expected, there is a small gene family of CCDs with different cleavage sites and somewhat promiscuous substrate selection. Some CCDs are stereo-specific, for example, 9-cis epoxycarotenoids are the substrates for NCEDs (9-cis expoxy dioxygenases) that produce the precursor of ABA biosynthesis, xanthoxin. Both linear carotenoids (lycopene) and cyclic carotenoids are substrates for cleavage at various double bonds including the central 15-15 and eccentric 5-6, 7-8, 9-10, 9 -10, and 11-12 bonds. Some CCDs cleave both linear and cyclic carotenoids and may cleave the same molecule twice, e.g., both 9-10 and 9 -10 positions. 

Plant IPT genes have been identified from Arabidopsis,401-403 petunia,404 hop,405 and rice406 and constitute a small gene family. In contrast to Agrobacterium IPT, biochemical analysis revealed that plant IPT predominantly utilizes ATP and ADP rather than AMP as a prenyl acceptor401,405,406 and DMAPP as the donor396 (Figure 14). 

Voltage-gated Na channels isolated from mammalian central and peripheral neurons and cardiac myocytes are heterotrimeric complexes composed of a, 1, and P2 subunits (Catterall 1992, Malhotra et al 2001). 0 and ) 1 subunits have also been identified in skeletal muscle (Trimmer et al 1989, Yang et al 1993) while 2 has not. The a subunits encode a small gene family of at least 10 members (Plummer Meisler 1999). Recently, two additional members of the P subunit gene family, pi A 124... 

ACC synthase is the enzyme that converts methionine to ACC, the precursor to the plant hormone ethylene. ACC synthase genes are generally found as small gene families [71]. Several ACC synthase mRNAs have been found to increase in abundance in Pelargonium leaves, apple and potato shoots, and Arabidopsis, zucchini, cucumber, mungbean, and rice... 

Some but not all of the maize enzymes are encoded by small gene families. It will be critical to dissect the role of gene family members in contributing to tissue-... 

Clones of cDNAs have been isolated from pea (7), spinach (8) and Mesembryanthemum crystallinum (9). The deduced amino acid sequences are approximately 90% identical, a high level of similarity. A small gene family, probably two or three copies (7,8,9), encodes the FNR precursor. This 43 kDa precursor, of 360 amino acids in peas, is processed after import by the chloroplast to its mature size of 35kDa by removal of a 52 amino acid transit peptide (7). 

The genetic basis of the multiple subunits is now established and in dicotyledons there is a small gene family encoding three or four GS polypeptides (Cullimore et al, 1984 Donn et al, 1984 Gebhardt et al, 1986 Hirel et al, 1987 Tingey and Coruzzi, 1987 Tingey et al, 1987 Tischer et al.. 1986). 

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