REL-homology region

J. Jain, E. Burgeon, T. M. Badalian, P. G. Hogan, and A. Rao. A similar DNA-binding motif in NFAT family proteins and the Rel homology region. J Biol Chem, 270, 4138-4145, 1995. 

Rel proteins contain a 280-amino acid homology region, which mediates both DNA binding and dimerization. DNA contact regions are located in the amino-terminal half and the residues responsible for the dimerization reside in the carboxy terminal half. 

Edelman (1970) proposed that each of the homology regions was separately folded into compact globular domains joined by relatively linear stretches of amino acids. Moreover, these domains evolved for specific funtions. Thus the Vh and Vl domains interact to form the antigen-combining site. The functions of the constant domains are the subject of this chapter. 

A film of the branched chain 5-methylhexyl polymer absorbed at 315 nm and the position of this maximum was relatively insensitive to temperature. Likewise, no thermal transition was observed in the region where the side chain melting transition was seen for PDHS and its higher homologs. 

Despite the similar functions of each isozyme, only two regions of amino acid homology exist (X and Y), one of 150 and a second of 120 amino acid residues, which are 54% and 42% identical among the isozymes but are differentially localized within each enzyme (Fig. 20-3). The X and Y domains form the catalytic core of the enzyme. A characteristic of the (3 and 8 isoforms is that relatively few amino acids (40-110) separate the X and Y entities, whereas a much larger separation is observed for the PLCy isoform (approx. 400). In addition, in PLCy, the region between X and Y contains amino acid sequences that are found in nonreceptor tyrosine kinases (SH2 and SH3 domains). All four isoforms possess pleckstrin homology (PH) domains. The latter are considered to enable the enzyme to become tethered to the plasmalemma via an interaction with PI(4,5)P2. In addition, all PLC isoforms possess an E-F hand domain, which is located between PH and X domains, and a C2 domain, which is located close to the Y domain. 

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