Development of a pyrG mutant of Aspergillus oryzae strain S1 as a host for the production of heterologous proteins.

The ease with which auxotrophic strains and genes that complement them can be manipulated, as well as the stability of auxotrophic selection systems, are amongst the advantages of using auxotrophic markers to produce heterologous proteins. Most auxotrophic markers in Aspergillus oryzae originate from chemical or physical mutagenesis that may yield undesirable mutations along with the mutation of interest. An auxotrophic A. oryzae strain S1 was generated by deleting the orotidine-5'-monophosphate decarboxylase gene (pyrG) by targeted gene replacement. The uridine requirement of the resulting strain GR6 pyrGΔ0 was complemented by plasmids carrying a pyrG gene from either Aspergillus nidulans or A. oryzae. ß -Galactosidase expression by strain GR6 pyrGΔ0 transformed with an A. niger plasmid encoding a heterologous ß -galactosidase was at least 150 times more than that obtained with the untransformed strain. Targeted gene replacement is thus an efficient way of developing auxotrophic mutants in A. oryzae and the auxotrophic strain GR6 pyrGΔ0 facilitated the production of a heterologous protein in this fungus.

Estimation of background radiation doses for the Peninsular Malaysia's population by ESR dosimetry of tooth enamel.

Background radiation dose is used in dosimetry for estimating occupational doses of radiation workers or determining radiation dose of an individual following accidental exposure. In the present study, the absorbed dose and the background radiation level are determined using the electron spin resonance (ESR) method on tooth samples. The effect of using different tooth surfaces and teeth exposed with single medical X-rays on the absorbed dose are also evaluated. A total of 48 molars of position 6-8 were collected from 13 district hospitals in Peninsular Malaysia. Thirty-six teeth had not been exposed to any excessive radiation, and 12 teeth had been directly exposed to a single X-ray dose during medical treatment prior to extraction. There was no significant effect of tooth surfaces and exposure with single X-rays on the measured absorbed dose of an individual. The mean measured absorbed dose of the population is 34 ± 6.2 mGy, with an average tooth enamel age of 39 years. From the slope of a regression line, the estimated annual background dose for Peninsular Malaysia is 0.6 ± 0.3 mGy y(-1). This value is slightly lower than the yearly background dose for Malaysia, and the radiation background dose is established by ESR tooth measurements on samples from India and Russia.

Blood transport method for chromosome analysis of residents living near Semipalatinsk nuclear test site.

A study was conducted to compare the storage conditions and transportation period for blood samples collected from residents living in areas near the Semipalatinsk nuclear test site (SNTS). Experiments were performed to simulate storage and shipping environments. Phytohaemagglutinin (PHA)-stimulated blood was stored in 15-ml tubes (condition A: current transport method) in the absence or in 50-ml flasks (condition B: previous transport method) in the presence of RPMI-1640 and 20% fetal bovine serum (FBS). Samples were kept refrigerated at 4 degrees C and cell viability was assessed after 3, 8, 12 and 14 days of storage. RPMI-1640, 20% FBS and further PHA were added to blood samples under condition A in 50-ml flasks for culture. Whole-blood samples under condition B were directly incubated without further sub-culturing process, neither media nor PHA were added, to adopt a similar protocol to that employed in the previous transport method. Samples in condition A and condition B were incubated for 48 hr at 37 degrees C and their mitotic index was determined. The results showed that viable lymphocytes were consistent in both storage conditions but the mitotic index was higher in condition A than in condition B. Although further confirmation studies have to be carried out, previous chromosomal studies and the present experiment have shown that PHA-stimulated blood could be stored without culture medium for up to 8 days under condition A. The present results will be useful for cytogenetic analysis of blood samples that have been transported long distances wherever a radiation accident has occurred.