DNA polymerase activity in encysting Entamoeba invadens

Using an axenic encystation system of Entamoeba invadens as a model for E. histolytica encystation, we examined the level of DNA polymerase activity i n E. invadens during encystation induced in vitro. We first characterized t he DNA polymerase activity of trophozoites of E. invadens, comparing it wit h that of E. histolytica, and found that the activity of E. invadens was lo wer than that of E. histolytica at pH 2, 4, and 6 and was higher at pH 8 an d 10. The activity of E. invadens was completely inhibited by high concentr ations of K+. Among inhibitors of mammalian DNA polymerases, aphidicolin an d N-ethylmaleimide inhibited the activity, but 2',3'-dideoxythymidine-5'-tr iphosphate did not. Thus, the sensitivity of the E. invadens activity to sa lt and inhibitors of mammalian DNA polymerases was basically the same as th at recorded for E. histolytica in our previous results. The level of DNA po lymerase activity in cysts decreased as encystation proceeded as compared w ith that of trophozoites. The results indicate that encystation is accompan ied by a reduced level of DNA polymerase activity, which correlates with th e previous finding that nuclear division occurs during cyst maturation in t he absence of DNA synthesis.