Prediction of splice sites in plant pre-mRNA from sequence properties.

Heterologous introns are often inaccurately or inefficiently processed in higher plants. The precise features that distinguish the process of pre-mRNA splicing in plants from splicing in yeast and mammals are unclear. One contributing factor is the prominent base compositional contrast between U-rich plant introns and flanking G + C-rich exons.

A combinatorial role for exon, intron and splice site sequences in splicing in maize.

Plant introns are typically AU-rich or U-rich, and this feature has been shown to be important for splicing. In maize, however, about 20% of the introns exceed 50% GC, and most of them are efficiently spliced. A series of constructs has been designed to analyze the cis requirements for splicing of the GC-rich Bz2 maize intron and two other GC-rich intron derivatives.

Cellulase induction in Trichoderma reesei by cellulose requires its own basal expression.

The induction of cellulases by cellulose, an insoluble polymer, in the filamentous fungus Trichoderma reesei is puzzling. We previously proposed a mechanism that is based on the presence of low levels of cellulase in the uninduced fungus; this basal cellulase activity would digest cellulose-releasing oligosaccharides that could enter the cell and trigger expression of cellulases. We now present experiments that lend further support to this model.

Two regulatory regions controlling basal and cellulose-induced expression of the gene encoding cellobiohydrolase I of Trichoderma reesei are adjacent to its TATA box.

The cellulolytic system of the filamentous fungus Trichoderma reesei is transcriptionally induced in the presence of the insoluble polymer cellulose. Previous studies have demonstrated that induction of the cellulose transcripts by cellulose requires basal expression of its own genes. To understand how basal expression controls cellulose-induced transcription of those genes, we analyzed the 5'-flanking region of the gene encoding cellobiohydrolase I (cbh1), the major member of the cellulase system, for the cis-acting region that is responsible for regulating basal and cellulose-stimulated expression.

Mutants of Trichoderma reesei are defective in cellulose induction, but not basal expression of cellulase-encoding genes.

Four mutants of Trichoderma reesei defective in cellulose utilization were characterized at the molecular level. Genomic analysis of the cellulase-encoding genes (cel) and transcript induction using two well-established inducers of the cel system--the insoluble polymer, cellulose and the soluble inducer, sophorose,--revealed that these mutants are defective in the transcription of cel genes. The results also indicate that the cel genes are coordinately expressed and most probably are regulated by the same mechanism.