Novel alleles of yeast hexokinase PII with distinct effects on catalytic activity and catabolite repression of SUC2.

In the yeast Saccharomyces cerevisiae, glucose or fructose represses the expression of a large number of genes. The phosphorylation of glucose or fructose is catalysed by hexokinase PI (Hxk1), hexokinase PII (Hxk2) and a specific glucokinase (Glk1). The authors have shown previously that either Hxk1 or Hxk2 is sufficient for a rapid, sugar-induced disappearance of catabolite-repressible mRNAs (short-term catabolite repression).

During the initiation of fermentation overexpression of hexokinase PII in yeast transiently causes a similar deregulation of glycolysis as deletion of Tps1.

In the yeast Saccharomyces cerevisiae a novel control exerted by TPS1 (= GGS1 = FDP1 = BYP1 = CIF1 = GLC6 = TSS1)-encoded trehalose-6-phosphate synthase, is essential for restriction of glucose influx into glycolysis apparently by inhibiting hexokinase activity in vivo. We show that up to 50-fold overexpression of hexokinase does not noticeably affect growth on glucose or fructose in wild-type cells. However, it causes higher levels of glucose-6-phosphate, fructose-6-phosphate and also faster accumulation of fructose-1,6-bisphosphate during the initiation of fermentation.

The genomic structure of the murine alpha 4 integrin gene.

The VLA-4 (alpha 4 beta 1) integrin is a leukocyte glycoprotein involved in both cell-extracellular matrix and cell-cell interactions. We report here the cloning of the murine alpha 4 gene whose protein product is antigenically related to the human VLA-4 alpha chain. The alpha 4 m gene is about 75 kb long and consists of 28 exons, ranging in size from 46 bp (exon 13) to 437 bp (exon 1).

A regulatory element in the 5'UTR directs cell-specific expression of the mouse alpha 4 gene.

Transfection experiments showed that the mouse alpha 4 promoter contains a downstream element in its 5'UTR which is essential for efficient promoter activity. DNaseI footprinting and electrophoretic mobility shift assays (EMSA) demonstrated that the region from nt +113 to +148 can bind a cell type-specific factor (MIII-3) present in the alpha 4m expressing cell line L1210 but not in the non-expressing cell lines A9 and LMTK. Two consensus SP1 sites in this 5'UTR were recognised in L1210, A9 and LMTK, and with extracts from A9 and LMTK, an AP2-like protein was shown to bind a downstream AP2 site.

Stable expression of VLA-4 and increased maturation of the beta 1-integrin precursor after transfection of CHO cells with alpha 4m cDNA.

A full-length cDNA coding for the murine alpha 4 integrin subunit (alpha 4m) was transfected into CHO-K1 cells and cell lines that expressed VLA-4 at their surface as a result of the association of transfected alpha 4m with endogenous hamster beta 1 were selected. Functionality of the expressed alpha 4m beta 1 was shown by adhesion assays on VCAM-1 and antibody (anti-VCAM-1) inhibition. Pulse chase experiments indicated that transfection of the murine alpha 4 cDNA into CHO cells led to an increase in maturation and a decrease in degradation of the beta 1 precursor subunit compared to control CHO-K1 cells.