A cis-acting A-U sequence element induces kinetoplastid U-insertions.

A 34-nucleotide A-U sequence located immediately upstream of the editing sites of the Leishmania tarentolae cytochrome b mRNA induces a mitochondrial extract to insert U nucleotides independent of guide RNA. Insertions are localized to positions immediately 5' and 3' of the A-U sequence. When placed within an unedited mammalian transcript, the A-U sequence is sufficient to induce U-insertions. The sequence has a high degree of similarity with the templating nucleotides of a cytochrome b guide RNA and with a sequence adjacent to the editing sites in ND7 mRNA, the other characterized kinetoplastid mRNA supporting guide RNA-independent U-insertions. At least one protein specifically interacts with the A-U sequence. The reaction is consistent with a mechanism proposed for guide RNA-directed editing.

Reproductive potential of vincristine-treated multinucleate carcinoma cells.

Multinucleate cells (MNC) form in a number of tumor cell lines treated with vincristine (VCR) and constitute the major difference between cell lines in which the affected cells survive VCR treatment and those in which the affected cells perish. We investigated the cell cycle traverse and proliferative potential of MNC which form among rat tracheal squamous carcinoma cells. Continuous-labeling curves for VCR-treated mononucleate and multinucleate cells were similar to those of untreated cells, and VCR-treated MNC survived for at least 7 days in culture. Observation of individual MNC, however, revealed no cytokinesis or continued proliferation. We conclude that although MNC arising after VCR treatment are capable of cell cycle traverse and prolonged survival in vitro, they are incapable of proliferation and, therefore, would not contribute to tumor regrowth.