Biomedical Engineering Reference
In-Depth Information
(GenBank D88750),
Drosophila melanogaster
(GenBank AE003694),
Homo
sapiens
(GenBank BC008326) and
Mus musculus
(GenBank M75107).
In contrast to cellulase genes, relatively few fungal β-galactosidase
encoding genes have been identifi ed. Examples in the databases to date
include gene sequence data from a number of
Aspergillus
species (
A.
fumigatus
, GenBank BX649607;
A. nidulans
, GenBank AACD01000005;
A.
Candidus
GenBank CAD24293 and
A. niger
GenBank L06037),
Hypocrea
jecorina
(GenBank AJ549427),
Penicillium sp.
(GenBank AJ629057),
Penicillium
canescens
(GenBank AJ629057) and
Talaromyces emersonii
(GenBank
AF439737). As the number of genome sequences increases it is conceivable
that the number of identifi able β-galactosidase genes from various sources
will increase. Of the fungal genes present in the database, the
Penicillium
sp.
gene is represented by 3610 bp open reading frame interrupted by 6
introns and encodes a 1011 amino acid protein with a deduced molecular
weight of 120 kDa. The
Penicillium canescens
gene is also interrupted by 6
introns and encodes a 1011 amino acid protein with a deduced molecular
mass of 109.75 kDa. The
A. oryzae
b-galactosidase gene which is interrupted
by 8 introns, encodes a 1005 amino acid protein, with a deduced molecular
mass of 109.898 kDa. The
Hypocrea jecorina
gene encodes a 1023 amino acid
b-galactosidase, with a deduced molecular weight of 111.368 kDa. It contains
a 3,523 bp open reading frame interrupted by seven introns.
REGULATION OF FUNGAL
β
-GALACTOSIDASE
GENE EXPRESSION
Carbohydrate hydrolyzing enzymes are secreted by fungi to supply
nutrients and energy to the growing microbe during growth on complex
plant material. In the presence of an easily metabolizable carbon source,
production and secretion of these enzymes would not be necessary. Thus,
regulation of gene expression is critical to the viability of the actively
growing fungus. In general carbohydrase induction is a complex process
with the level of response to individual inducers varying depending on
the organism (Hrmova et al. 1989). It is believed that substrate derivatives
and/or enzymatic end products play positive roles in the induction of
carbohydrate degrading enzymes; they can also, however, act as inhibitors
at higher concentrations.
High molecular mass plant material cannot penetrate the microbial
cell wall. Therefore, low molecular mass fragments play a key role in the
regulation of enzyme biosynthesis. It is generally believed that low levels of
constitutively expressed enzymes are secreted or released into the growing
medium or are bound to the conidial surface. These enzymes act on plant
polymers producing signalling molecules, which are taken up by the cell
