M. Czyz et al., AUTOREGULATION OF GAL4 TRANSCRIPTION IS ESSENTIAL FOR RAPID GROWTH OFKLUYVEROMYCES-LACTIS ON LACTOSE AND GALACTOSE, Nucleic acids research, 21(18), 1993, pp. 4378-4382
Transcriptional induction of genes in the lactose-galactose regulon of
the yeast Kluyveromyces lactis requires the GAL4 transcription activa
tor protein. Previous data indicated that the concentration of GAL4 wa
s tightly regulated under basal, inducing, and glucose repressing cond
itions but the mechanisms were unknown. In this paper we demonstrate t
hat transcription of the GAL4 gene (Kl-GAL4) increases 3- to 4-fold du
ring induction of the regulon. This increase requires a Kl-GAL4 bindin
g site, UAS(G), in front of the Kl-GAL4 gene, indicating that the Kl-G
AL4 protein autoregulates transcription of its own gene. Our data demo
nstrate that the autoregulatory circuit is essential for full inductio
n of the lactose-galactose regulon and, hence, for rapid growth on lac
tose or galactose. Other data indicate that basal transcription of the
Kl-GAL4 gene is governed by unidentified promoter elements. The exist
ence of the autoregulatory circuit reveals an important difference bet
ween the lactose-galactose regulon and its homologue in Saccharomyces
cerevisiae, the melibiose-galactose regulon. This difference may have
evolved in response to different selective pressures encountered by th
e two organisms.