Ronald C. Rustad

The incorporation of [14C] uracil and [14C] orotic acid into RNA in the cytoplasm of Amoeba proteus.

Abstract Nucleate and anucleate halves of Amoeba proteus were incubated with [ 14 C] uracil and [ 14 C] orotic acid. Autoradiographic analysis of cells after varying incubation periods indicated that both of these precursors were incorporated into cytoplasmic RNA in both nucleate and anucleate cells. It is suggested that the extensive incorporation of orotic acid derivatives into cytoplasmic RNA in anucleate cells represents good evidence for the capability of the cytoplasm for RNA synthesis in the absence of the nucleus.

Nuclear-cytoplasmic relations in the mitosis of sea urchin eggs.

Hartmann (1924, 1928), Phelps (1926), and Prescott (1956) have reported an inhibition of mitosis in amoeba by repeated cytoplasmic amputation. These observations suggest either a direct cytoplasmic control of mitosis or an interaction between the cytoplasm and the nucleus leading to an inhibition of the nuclear cycle. However, this pattern of division inhibition does not appear to be applicable to the ciliate Blepharisma undulans (Hirshfield and Pecora, 1956). In order to test further the generality of the hypothesis that the removal of a significant amount of cytoplasm leads to mitotic delay, we have examined the first division cycle of the sea urchin egg. A small regulative egg appears to be the logical extreme for a test organism, because there is no net cytoplasmic growth and a normal interphase may be lacking. The relatively constant lengths of the second, third, and fourth mitotic cycles (for example, Harvey, 1956) indicate that the amount of cytoplasm per se does not determine the division rate.