Macromolecule synthesis in temperature-sensitive mutants of methanol-utilizing Hansenula polymorpha

Temperature sensitive (ts) mutants of methanol-utilizing Hansenula polymorpha NTU-AM-P5 were isolated by UV irradiation, EMS and/or NTG treatment. They grow normally at permissive temperature (PT) 38 degrees C, but can not grow at restrictive temperature (RT) 46 degrees C. From chemical composition analysis, it was found that ts mutants NTU-AM-L2 and NTU-AM-L3 had higher RNA content than the others; while ts mutant NTU-AM-E19 had the highest protein content among the isolated strains. Leucinyl-tRNA synthetases activity was the highest among the twenty aminoacyl-tRNA synthetases in both wild type and their ts mutants. When the cells were shifted from PT to RT for 12 h, total aminoacyl-tRNA synthetase activity decreased in all tested strains. Leucinyl-tRNA synthetase of ts mutant NTU-AM-E10 decreased 91.23%. At RT, it was found that ts mutants NTU-AM-E10 and NTU-AM-E20 were defective in DNA synthesis; ts mutants NTU-AM-E15, NTU-AM-E20, NTU-AM-N37 and NTU-AM-m5 were defective in RNA synthesis; ts mutants NTU-AM-E10, NTU-AM-E20 and NTU-AM-m5 were somewhat defective in protein synthesis; while ts mutants NTU-AM-L2 and NTU-AM-L3 did not belong to any one of the above classifications.

Simultaneous in situ detection of beta-interferon mRNA and DNA in the same cell

We report a quantitative method that combines in situ mRNA hybridization with microfluorometric analysis of DNA content to detect gene expression in single cells of a heteroploid cell population. The model was a human fibrosarcoma HT1080 cell line which consisted of diploid and tetraploid cells that were induced with polyI:polyC for production of beta-interferon. The level of beta-interferon mRNA detected by in situ hybridization was found to be two to three times higher in tetraploid compared to diploid HT1080 cells, and correlated with beta-interferon activity in that a subclone of tetraploid HT1080 cells secreted two- to fivefold more beta-interferon than a subclone of diploid HT1080 cells. Interestingly, beta-interferon-related transcripts were detected during S-phase in uninduced tetraploid HT1080 cells. In addition, beta-interferon induced by polyI:polyC was expressed in all phases of the cell cycle as demonstrated with a human diploid fibroblast, HF926. The unique features offered by the combination of microfluorometry and in situ hybridization provide a valuable tool to investigate specific gene expression related to ploidy or cell-cycle stage in the same individual cell of an unsynchronized population. Since the method allows direct observation of morphology, one can be assured that all quantitative measurements were made on whole cells with intact nuclei.

Isolation and characterization of temperature-sensitive mutants of Hansenula

For investigation of the feasibility of obtaining yeast strains with high protein and low nucleic acid content or high nucleic acid and low protein content for industrial production of single cell protein or nucleotide, the methanol-utilizing Hansenula polymorpha NTU-AM-P5 was chosen for isolation of temperature-sensitive mutants. Approximately 70 temperature-sensitive (ts) mutants were obtained. All of the ts mutants increased in cell size and aggregated when they were cultivated at permissive temperature and shifted to restrictive temperature in the late log phase or in the stationary phase. 86.1% of ts mutants had a lower growth rate than that of their wild-type. Only ts mutants, NTU-AM-L2, NTU-AM-E10, NTU-AM-E19, NTU-AM-E25 and NTU-AM-E30 had same or slightly higher than that of their wild-type strain. Cycloheximide at 1 mg/ml inhibited the growth of ts mutant NTU-AM-E19, but inhibited one-third of the other ts mutants, and their wild-type strain. Rifampicin at 0.1 mg/ml had an inhibitory activity on wild-type strain but not on ts mutant NTU-AM-E1. ts mutants NTU-AM-L2 and NTU-AM-E19 converted methanol to cell mass more efficiently than others. The ts mutants divided into two groups. One included absolute ts mutants, such as NTU-AM-E15 and NTU-AM-E20, which did not grow even in enriched media at restrictive temperature; the other group, such as NTU-AM-L2, NTU-AM-L3, NTU-AM-E10, NTU-AM-E19, NTU-AM-N37 and NTU-AM-m5, was auxotrophic ts mutants, which grew slightly in enriched media at restrictive temperature.