The isolation of yeast nuclei and methods to study their properties

Casting new physicochemical light on the fundamental biological processes in single living cells by using Raman microspectroscopy

This Personal Account highlights the capabilities of spontaneous Raman microspectroscopy for studying fundamental biological processes in a single living cell. Raman microspectroscopy provides time- and space-resolved vibrational Raman spectra that contain detailed information on the structure and dynamics of biomolecules in a cell. By using yeast as a model system, we have made great progress in the development of this methodology. The results that we have obtained so far are described herein with an emphasis placed on how three cellular processes, that is, cell-division, respiration, and cell-death, are traced and elucidated with the use of time- and space-resolved structural information that is extracted from the Raman spectra. For cell-division, compositional- and structural changes of various biomolecules are observed during the course of the whole cell cycle. For respiration, the redox state of mitochondrial cytochromes, which is inferred from the resonance Raman bands of cytochromes, is used to evaluate the respiration activity of a single cell, as well as that of isolated mitochondrial particles. Special reference is made to the "Raman spectroscopic signature of life", which is a characteristic Raman band at 1602 cm(-1) that is found in yeast cells. This signature reflects the cellular metabolic activity and may serve as a measure of mitochondrial dysfunction. For cell-death, "cross-talk" between the mitochondria and the vacuole in a dying cell is suggested.

Identification and isolation of core histones from Schizosaccharomyces pombe

Core histones have been isolated from Schizosaccharomyces pombe and compared electrophoretically to core histones from Saccharomyces cerevisiae and rat liver. The molecular masses of all cognate histones examined were found to be very similar as determined by SDS gel electrophoresis. Histones H3, H2A and H2B from Sch. pombe migrated almost identically to their respective counterparts from S. cerevisiae as determined by acid/urea gel electrophoresis. Two-dimensional gel electrophoresis with a Triton X-100 acid/urea gel in the first dimension followed by an SDS gel in the second dimension was used to separate Sch. pombe histones from contaminating ribosomal proteins.

Biological properties and mode of action of clavams

The clavams valclavam and hydroxyethylclavam were both bacteriostatic and fungistatic. The molecular basis for growth inhibition of Escherichia coli was a non-competitive inhibition of homoserine-O-succinyltransferase (EC 2.3.1.46), thus blocking methionine biosynthesis. Eucaryotes such as Saccharomyces cerevisiae were inhibited by a different mode of action. Instead of interfering with methionine biosynthesis, the clavams inhibited the formation of RNA in living cells, although the RNA-polymerases of isolated yeast nuclei were not inhibited. The action of valclavam on E. coli was dependent on functional peptide transport systems.

The organization of oligonucleosomes in yeast

We have developed a method of preparing yeast chromatin that facilitates the analysis of nucleoprotein organization. Yeast chromatin, isolated as an insoluble complex, is digested with micrococcal nuclease and fractionated into major insoluble and soluble fractions. No nucleosomal repeat is seen early in digestion for the insoluble fraction. Nucleosomal complexes of the soluble fraction are excised by nuclease in a distinctive non-random pattern; they are markedly depleted in mononucleosomes. When we analyze the soluble material by high resolution native electrophoresis, we find that the nucleoproteins resolve into two bands for each DNA multimer of the nucleosomal repeat. Our results suggest that there are structural similarities between bulk yeast chromatin and chromatin configurations found in transcribing genes of complex eukaryotes.

Nuclear localization of aspartate transcabamoylase in Saccharomyces cerevisiae

The cytochemical technique using the in situ precipitation of orthophosphate ions liberated specifically by the aspartate carbamoyltransferase (ATCase) (EC 2.1.3.2) reaction indicated that in Saccharomyces cerevisiae this enzyme is confined to the nucleus. This observation is in accordance with the result reported by Bernhardt and Davis (1972), Proc. Natl. Acad. Sci. U. S. A. 69:1868-1872) on Neurospora crassa. The nuclear compartmentation was also observed in a mutant strain lacking proteinase B activity. This finding indicates that this proteinase is not involved in the nuclear accumulation of ATCase, and that the activity observed in the nucleus corresponds to the multifunctional form associated with the uracil path-specific carbamoylphosphate synthetase and sensitive to feedback inhibition by UTP. In a ura2 strain transformed by nonintegrated pFL1 plasmids bearing the URA2-ATCase activity encoding gene, the lead phosphate precipitate was observed predominantly in the cytoplasm. This finding enhances the reliability of the technique used by eliminating the possibility of an artifactual displacement of an originally cytoplasmic reaction product during the preparation of the material for electron microscopy. On the other hand, nuclei isolated under hypoosmotic conditions do not exhibit the ATCase activity that is recovered in the cytosolic fractions after differential centrifugation of the lysate in Percoll gradient. A release of the protein from the nuclei during the lysis step, consistent with its nucleoplasmic localization, is postulated.

Purification and properties of an endonuclease from the mitochondrion of Saccharomyces cerevisiae

An endonuclease, which is found only in the mitochondrion of the yeast Saccharomyces cerevisiae, has been purified. The protein has a sedimentation coefficient of 6.3 S, equivalent to a molecular weight of 105,000. The enzyme is active at pH 7.6, when it degrades single-stranded DNA about 10-times faster than double-stranded DNA, but at pH 5.4 only double-stranded DNA is degraded. In both cases the enzyme acts endonucleolytically, breaking a single phosphodiester bond at a random location within the DNA substrate. Mn2+ or Mg2+ are required for activity; Ca2+ and Zn2+ are ineffective cofactors. Enzyme activity at pH 7.6 is severely inhibited by low concentrations of NaCl or KCl, while activity at pH 5.4 is unaffected by salt. Ethidium bromide inhibits both the DNase activity at pH 5.4 and the activity with single-stranded DNA at pH 7.6, but has no effect on the DNase activity with double-stranded DNA at pH 7.6.