The signal for glucose repression of the lactose-galactose regulon is amplified through subtle modulation of transcription of the Kluyveromyces lactis Kl-GAL4 activator gene.

Abstract

Induction of the lactose-galactose regulon is strongly repressed by glucose in some but not all strains of Kluyveromyces lactis. We show here that in strongly repressed strains, two to three times less Kl-GAL4 mRNA is synthesized and that expression of structural genes in the regulon such as LAC4, the structural gene for 13-galactosidase lactose-galactose regulon. Strains such as Y1140 show weak repression because the fully induced level of the regulon, as measured by 0-galactosidase activity, is reduced only twofold by the presence of glucose in the culture medium (7). Strains such as CBS2360 show almost no repression (2), while strains such as JA6 (2) and Y1118 (this report) show strong (50-to 100-fold) repression of the regulon by glucose under inducing conditions. How might glucose affect expression of the regulon? Initial insight into the mechanism of glucose repression was provided by Breunig (2), who showed that a glucose-repressing strain could be converted to a nonrepressing strain by changing the allele carried at the K1-GAL4 locus (also called LAC9 [27]).Kl-GAL4 codes for a transcription activator protein that regulates and is essential for transcription of the lactosegalactose regulon (33). The Kl-GAL4 protein binds to a family of 17-bp DNA sequences, termed upstream activator sequences (UASG; the G refers to the lactose-galactose regulon), located in front of genes comprising the lactosegalactose regulon (3,9,17,25

Centromere promoter factors (CPF1) of the yeasts Saccharomyces cerevisiae and Kluyveromyces lactis are functionally exchangeable, despite low overall homology

“…Nevertheless, each displays a characteristic lifestyle and metabolism, indicative of the existence of perhaps widespread differences in regulatory patterns. Such differences have indeed been confirmed both at the level of individual metabolic pathways (Kuzhandaivelu et al 1992;Mazzoni et al 1992;Wdsolowski-Louvel et al 1992) and of the sequence/structure of an increasing number of regulatory proteins (Gon~alves et al 1992;Na and Hampsey 1993;Zachariae and Breunig 1993;Mulder et al 1994). Strikingly, despite sometimes quite extensive differences in sequence and overall organisation, the K. lactis proteins often appear to be functionally homologous to their S. cerevisiae counterparts, as evidenced by the fact that their coding sequences have been isolated by the technique of functional complementation of the appropriate S. cerevisiae null mutant.…”

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

“…However, the regulation of invertase in K lactis has not been studied much, and it is not known yet whether it is sensitive to glucose repression. In this yeast, the synthesis of 3-galactosidase inducible by galactose and lactose has been reported to be sensitive to glucose in some strains but not in others (7,25).…”

Influence of Mutations in Hexose‐Transporter Genes on Glucose Repression in Kluyveromyces Lactis

“…The dynamics of P-galactosidase induction suggests that in the kht single mutants some activation of Gal4p occurs in response to galactose but then induction of GAL80 gene expression prevents the inducing signal from being amplified (Zachariae, 1994). Since in JA6 cells grown in 2% glucose and 2 % galactose the induction and repression pathways are in a delicate equilibrium Kuzhandaivelu et al, 1992) even a small change in the ratio of glucose to galactose uptake can have an influence on the dynamics of induction. Here the inhibition of 8-galactosidase induction served as a sensitive measure for glucose uptake.…”

“…Moreover, there is considerable variability among K. lactis strains with respect to glucose repression and some strains show no repression at all (Ferrero et a]., 1978;Breunig, 1989). A comparison between strains already revealed genetic determinants responsible for differences in glucose repression of lactose and galactose metabolism (Kuzhandaivelu et al, 1992;Zachariae et al, 1993). Here we have addressed the question of whether there is any causal relationship between the sensitivity to glucose repression and the dependence on oxidative phosphorylation.…”