The invention provides the nucleotide sequence of a novel .beta.-(1,3)
exoglucanase gene denoted as cbeg1 of the soil-borne fungus Coniothyrium
minitans. The deduced amino acid sequence of the encoded .beta.-(1,3)
exoglucanase enzyme, denoted Cbeg1, is also provided. Encoded .beta.-(1,3)
exoglucanase Cbeg1 is specific for the substrate laminarin, in that
results showed no activity with other substrates tested, such as
carboxymethylcellulose, barley .beta.-glucan, lichenan, oat spelt xylan
and birchwood xylan. The pH and temperature optima for .beta.-(1,3)
exoglucanase Cbeg1 are 6.0 and 57.degree. C., respectively. Cbeg1 contains
784 amino acids, and has a predicted isoelectric point (pI) of 6.0 and
molecular weight of 83,646 Daltons. The invention further provides vectors
and cells comprising a nucleic acid molecule encoding the cbeg1 gene, and
methods for producing .beta.-(1,3) exoglucanase Cbeg1. The cbeg1 gene is
compatible with a eukaryotic heterologous expression system, making it
particularly useful for a wide range of industrial applications, such as
improvement of plant resistance to fungal phytopathogens or use in
ruminant microbial transgenic strategies to improve feed digestion and
nutritive carbohydrate availability from forage feed. In addition, the
high activity of Cbeg1 over broad pH and temperature ranges may be
beneficial for use in high temperature industrial applications, such as
bleaching of pulp, which require temperatures greater than 37.degree. C.
Further, Cbeg1 may complement degradation initiated by endoglucanases
which release oligoglucans, in that .beta.-(1,3) exoglucanase sequentially
hydrolyzes .beta.-(1,3) glucan fragments and is required to hydrolyze
oligoglucan fragments completely to obtain D-glucose, which can be
assimilated.
