Yeast mRNA flux during brewing and under ethanol stress conditions

Abstract

Yeast is a eukaryotic cell in which transcription (the nucleus) is separated from translation (the cytoplasm) by the nuclear membrane. The synthesized mRNA of yeast is translated through various steps, such as intranuclear processing and nuclear export. Various cytoplasmic processes, such as mRNA degradation and the formation of mRNP granules, are also involved in the regulation of gene expression. Thus, the expression of genes in yeast should be understood as a series of steps (mRNA flux) that include the processing, transport, translation, and degradation of mRNA, as well as transcriptional regulation. Yeast mRNA undergoes capping, poly (A) tailing, and splicing, and also forms mRNP complexes with mRNA export factors in the nucleus, which are then exported from the nucleus into the cytoplasm. However, under heat-shock conditions (42 °C), the transport of nonessential mRNAs is suppressed whereas various HSP mRNAs are preferentially transported in yeast cells (i.e., selective nuclear export of mRNA). Not all mRNAs are translated following their cytoplasmic transport; the expression of some mRNAs is regulated by processes such as translational repression or degradation, and is dependent on the conditions present. Untranslated mRNAs leave ribosomes under various stress conditions and form cytoplasmic mRNP granules (processing bodies and stress granules) with mRNA-degrading enzymes or translation factors. Untranslated mRNAs are sequestered from the translation apparatus in processing bodies and stress granules during stress responsive translational regulation. A recent study demonstrated the unique phenomena of mRNA nuclear export and translational regulation under ethanol stress conditions or during brewing. I herein describe yeast mRNA flux, which was found to be tightly regulated at various steps.