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

N. Kuzhandaivelu, W. K. Jones, A. K. Martin, R. C. Dickson

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

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 β-galactosidase, is down regulated 40-fold or more. Comparative analysis of strains having a strong or weak repression phenotype revealed a two-base difference in the promoter of the Kl-GAL4 (also called LAC9) positive regulatory gene. This two-base difference is responsible for the strong versus the weak repression phenotype. The two base changes are symmetrically located in a DNA sequence having partial twofold rotational symmetry (14 of 21 bases). We hypothesize that this region functions as a sensitive regulatory switch, an upstream repressor sequence (URS). According to our model, the presence of glucose in the culture medium signals, by an unidentified pathway, a repressor protein to bind the URS. Binding reduces transcription of the Kl-GAL4 gene so that the concentration of the Kl-GAL4 protein falls below the level needed for induction of LAC4 and other genes in the regulon. For strains showing weak glucose repression, we hypothesize that the two base changes in the URS reduce repressor binding so that the regulon is not repressed. Our results illustrate an important principle of genetic regulation: a small (2- to 3-fold) change in the concentration of a regulatory protein can produce a large (40-fold or greater) change in expression of structural genes. This mechanism of signal amplification could play a role in many biological phenomena that require regulated transcription.

Original languageEnglish
Pages (from-to)1924-1931
Number of pages8
JournalMolecular and Cellular Biology
Volume12
Issue number5
DOIs
StatePublished - 1992

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

Fingerprint

Dive into the research topics of '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'. Together they form a unique fingerprint.

Cite this