Biology Reference
In-Depth Information
Ancestor NR gene
SUBFAMILY I
THR, RAR, THRAL
SUBFAMILY III
Steroid receptors
SUBFAMILY II
Orphan receptors
Ancestor to
THRs and
RARs
Steroid receptor
genes
Ancestor to
VDR gene
Ancestor to
THRAL
and
related genes
THR/RAR gene complex
on the same chromosome
RARG
12q13
THRA
17q21
RARA
17q21
E domain
for VDR
Duplication
of C domains
E domain from
subfamily I genes
PPAR
THRB
3p24
RARB
3p24
THRAL
Chimeric VDR
Translocation of
THRAL
gene
in the C-terminal part of the
THRA
locus
Figure 4.28.
Evolutionary schema for the human nuclear receptor genes (redrawn from
Laudet
et al
., 1992).
al
., 1992;
Figure 4.28
). An E domain from subfamily I has been been acquired by
the
VDR
gene which distinguishes it from the other genes in the steroid hormone
receptor family (Laudet
et al
., 1992;
Figure 4.28
). There appears however to be no
relationship between the phylogenetic position of a liganded receptor and the
chemical nature of its ligand (Escriva
et al
., 1997).
Protein kinase C genes
. The members of the mammalian protein kinase C
superfamily are involved in a number of signalling systems underlying a range of
cellular processes. The characterized members of the human superfamily can be
divided into three subfamilies, class I:
(
PRKCA
; 17q22-q23),
(
PRKCB1
;
16p11) and
(
PRKCG
; 19q13), class II:
(
PRKCD
; 3p) and
(
PRKCQ
; 10p15),
class III:
(
PRKCZ
). These genes
have an ancient origin, their homologues having been found in both nematode
and yeast (Mellor and Parker, 1998). The deduced amino acid sequences are
highly conserved among mammals (>95% homology between humans and
rodents) although homology is lower (45-65%) between nematodes and mam-
mals. The expression pattern of the different proteins can however vary markedly.
Structurally, each subfamily is characterized by a different arrangement of regula-
tory domains which serve to determine signalling specificity (Mellor and Parker,
1998).
(
PRKCE
), class IV:
(
PRKCI
; Xq21.3), and
Serine protease genes.
The serine protease superfamily provide an archetypal
example of evolution by gene duplication and divergence coupled with exon
