Positive and Negative Transcriptional Control by Heme of Genes Encoding 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in Saccharomyces cerevisiae

Abstract

Responses of the yeast genes encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase, HMG1 and HMG2, to in vivo changes in heme concentrations were investigated. Expression of the genes was determined by direct measurement of the mRNA transcribed from each gene, by direct assay of the enzyme activity encoded by each gene, and by measurement of the expression of lacZ fusions to the control regions of each gene. These studies indicated that expression of HMG1 was stimulated by heme, whereas expression of HMG2 was repressed by heme. The effect of heme on HMG1 expression was mediated by the HAP1 transcriptional regulator and was independent of HAP2. Thus, the genes encoding the 3-hydroxy-3-methylglutaryl coenzyme A reductase isozymes join a growing list of gene pairs that are regulated by heme in opposite ways.

Comprehensive evaluation of isoprenoid biosynthesis regulation in Saccharomyces cerevisiae utilizing the Genome Reporter Matrix™

“…Both miconazole and sulconazole induced ARE1 expression and repressed ARE2 expression (Table 3). This opposing effect of a treatment on the two isozymes of an enzymatic activity has been seen before in the yeast sterol pathway (2,4). In contrast, fluconazole treatment induced both ARE1 and ARE2 (Table 3).…”

“…This feedback regulation is keyed to multiple intermediates and appears to act at numerous steps of the pathway, involving changes in transcription, translation, and protein stability. Additionally, the availability of molecular oxygen, required for sterol and heme biosynthesis, also regulates the expression of genes at key steps of the pathway (4,5). The emerging picture is that the isoprenoid pathway has numerous points of regulation that act to control overall flux through the pathway as well as the relative flux through various branches of the pathway.…”

Metabolic Engineering to Produce Sesquiterpenes in Yeast

“…23 S. cereVisiae encodes two isozymes of this protein, Hmg1p and Hmg2p. Although the yeast isozyme Hmg1p is regulated by transcription, 24 translation, 25 and ubiquitin-mediated proteolysis, 26 removing the noncatalytic N-terminal transmembrane-spanning domain (1656 nucleotides) from Hmg1p generates an active, cytosolic truncated protein. High-level expression of the truncated Hmg1p significantly increases accumulation of the sterol precursor squalene.…”

Biosynthesis of C5–C20terpenoid compounds

“…Thorsness et a/. 16 have shown that, in the presence of heme, expression of HMGl is stimulated whereas HMG2 is repressed. This effect is not uncommon for pairs of genes which encode isozymes.…”

“…g OGlc have examined the biosynthesis of dihydrocornin (16) and cornin (17) in whole plants of Verbena oficinalis. In a comprehensive study, I3Clabelled 8-hydroxygeraniol (12), iridial (13), iridotrial (14), deoxyloganin (13, and other putative precursors were synthesized and fed.…”