Abstract: BACKGROUND ＆ AIM: To study the mechanism of injury on the fetus and infants in the brain development caused by methly mercury chloride(MMC) and its effects on the transcription activities of three RNA polymerase in the brain nuclei by MMC with experiments in vitro and in vivo. MATERIAL AND METHODS: In vivo，Wistar pregnant rats were administered with 4 mg/kg MMC of body weight by gastric perfused from the 7th to the 9th gestational days. On the 3rd , 7th,14th,21st and 30th days after birth,the rats were killed and the nuclei were harvested from their brain; in vitro, used Dnase I、EcoR I digestion for nick translation to observed the effect of MMC by scintillation counting, of 3H-dAMP. The effect to the activity of three RNA polymerase was also observed by scintillation counting, of 3H-UMP. RESULTS: The 3rd and 7th days after birth 3H-dAMP incorporation of brain nuclei were significantly lower than that of unexposed rats (P<0.01). The activity of three sorts of RNA polymerase was inhibited too. CONCLUSION:It is concluded that MMC could inhibit the translation activity of brain nuclei and the three RNA polymerases, which could explain the mechanism of inhibition to the protein synthesis.

Key words: methyl mercury chloride, brain nuclei, chromatin, RNA polymerase