Role of heme in mitochondrial biogensis: Transcriptional and post-transcriptional regulation of the expression of Iso-l-cytochrome C gene during glucose repression-derepression in cells of Saccharomyces cerevisiae.

Exogenous addition of hemin to glucose-repressed cells of Saccharomyces cerevisiae restores the level of Iso-1-cytochrome C messengers to that observed in derepressed cells. In vitro transcription in isolated nuclei has shown a 4-fold stimulation in the synthesis of Iso-1-cytochrome C messengers in repressed but hemin-treated and derepressed cells compared to the repressed cells. Studies on in vitro transport of RNA from isolated nuclei have revealed that there is a 50% drop in the transport of total RNA from nuclei isolated from repressed but hemin-treated and derepressed cells when compared with the nuclei from repressed cells. However, under these conditions, there is an enhanced transport of translatable RNA. Hybridization analysis of the transported RNA using Iso-1-cytochrome C gene-specific probe has shown that there is preferential transport of Iso-1-cytochrome C messengers in repressed but hemin treated and derepressed cells.

Mitochondrial RNA metabolism during mitochondriogenesis in yeast.

Mitochondrial transcription has been studied as a function of mitochondriogenesis in yeast cells. Two systems have been used: synchronously growing cells and cells subjected to glucose repression followed by derepression. Maximal RNA synthesis has been found in the S phase of the cell cycle and during the 'repressed' phase in asynchronous cells. Activities of RNA polymerase, poly A polymerase and incorporation of [32P]-into RNA in vitro are maximal at the same period. Gel analysis reveals the presence of some high molecular weight RNA species which are likely to be precursors. When chase experiments are carried out in the presence of excess glucose, the high molecular weight species remain unaffected, suggesting that RNA processing may be an important site of action of glucose repression.