Hap4 Is Not Essential for Activation of Respiration at Low Specific Growth Rates in Saccharomyces cerevisiae

Vijayendran Raghevendran,Kiran Raosaheb Patil,Lisbeth Olsson,Jens Nielsen

doi:10.1074/jbc.m512972200

Vijayendran Raghevendran, Kiran Raosaheb Patil + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m512972200

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Abstract

In Saccharomyces cerevisiae, the heme-activated protein complex Hap2/3/4/5 plays a major role in the transcription of genes involved in respiration. Thus, overexpression of HAP4 has been shown to result in a 10% increase in the respiratory capacity. Here the physiology of a HAP4-deleted S. cerevisiae strain was investigated, and we found that the hap4delta S. cerevisiae exhibited poor growth on ethanol, although the growth rate on glucose was indifferent from the wild type in aerobic as well as anaerobic cultures. Moreover, it exhibited a large (75%) reduction in the critical glucose uptake rate at which fermentative metabolism is onset, indicating a substantial reduction in respiratory capacity. We also performed whole genome transcription analysis for the hap4delta and the wild type, grown in carbon-limited chemostat cultures operated at a dilution rate of 0.05 h(-1). Although both strains exhibited respiratory metabolism, there was significant change in expression of many genes in the hap4delta strain. These genes are involved in several different parts of the metabolism, including oxidative stress response, peroxisomal functions, and energy generation. This study strongly indicates that Hap4 activation only occurs at intermediate specific growth rates, below which the transcription of genes responsible for respiration is dependent on the Hap2/3/5 complex and above which the Hap4 protein augments the transcription. Furthermore, statistical analysis of the transcription data and integration of the data with a genome scale metabolic network provided new insight and evidence for the role of Hap4 in transcriptional regulation of mitochondrial respiration.

Highlights

Eukaryotic model organism for studying human diseases, making it an attractive model for studying respiration
The results (Table 1) show the characteristic growth behavior of S. cerevisiae at high glucose uptake rates, i.e. there is fermentative metabolism with most of the carbon being directed toward ethanol with concomitant secretion of pyruvate, acetate, glycerol, and succinate
The results show that deletion of HAP4 had little or no effect on the specific growth rate, compared with the wild type both aerobically as well as anaerobically

Summary

Introduction

Eukaryotic model organism for studying human diseases, making it an attractive model for studying respiration. The promoter of HAP4 has three carbon source responsive elements [12], which require a functional Cat for the activation (a transcription factor that activates gluconeogenic genes); deletion of CAT8 had no effect on the steady state level of HAP4 expression [13]. It has not been proven in vivo that Mig binds to the HAP4 promoter even though it is generally accepted that HAP4 expression is under glucose repression via Mig. Deletion of MIG1 together with HAP4 overexpression was found to result in further derepression of the SUC2 gene compared with a mig1⌬ control [14], indicating a possible role of Hap in Mig1-mediated glucose repression

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