Biomedical Engineering Reference
In-Depth Information
(Fontes et al. 1993; Botella et al. 1995). The existence of more than one
gene for a particular biochemical function may be related to pathways,
tissues, subcellular compartments and/or different growth stages where
the respective proteins perform their functions.
The biosynthesis of carotenoids in
Phycomyces
is blocked by three kinds
of mutations
carA
,
carB
and
carR
(Meissner and Delbruk 1968, Avalos and
Cerdá-Olmedo 2004). As the wild-type is yellow due to accumulation of
β-carotene, mutants are easily identifi ed by simple visual inspection. The
carA
mutants are white, do not accumulate any carotenoid and are altered
in the enzyme phytoene synthase.
carB
mutants are white, accumulate
phytoene and are altered in the enzyme phytoene dehydrogenase. The
carR
mutants are red because they accumulate lycopene and are altered in
the enzyme lycopene cyclase. Genetic analysis of these mutants revealed
the existence of two closely linked genes,
carB
and
carRA
. The
carRA
is a
bifunctional gene with a 5' domain that codifi es for the lycopene cyclase
enzyme and a 3' domain that codifi es for the phytoene synthase enzyme
(Torres-Martinez et al. 1980). Similar results were found for
M. circinelloides
(Velayos et al. 1997, Ruiz-Hidalgo et al. 1995, Navarro et al. 1995) and
B.
trispora
(Mentha and Cerdá-Olmedo 1995).
carB
genes from
Phycomyces
(Ruiz-Hidalgo et al. 1997),
Mucor
(Velayos
et al. 2000a) and
Blakeslea
(Rodríguez-Sáiz et al. 2004) have been isolated
and sequenced from their
Neurospora
counterparts (Schmidhauser et al.
1990). The
Phycomyces carRA
(Arrach et al. 2001, Sanz 2004),
Mucor carRP
(Velayos et al. 2000b) and
Blakeslea carRA
(Rodríguez-Sáiz et al. 2004) genes
were obtained after the isolation of their homologue in
Xhantophyllomyces
(Verdoes et al. 1999b). In the three Mucorales
Phycomyces
,
Mucor
and
Blakeslea
the
carB
and
carRA/ P
genes are closely linked and divergently transcribed
(Table 1
and Figure 2).
Figure 2.
Organization of the phytoene synthase/lycopene cyclase (dark grey boxes)
and phytoene dehydrogenase (light grey boxes) coding genes in fungi.
