Transcriptional interference between genes and the regulatory elements of simple eukaryotes such as Saccharomyces cerevisiae is an unavoidable consequence of their compressed genetic arrangement. We have shown previously that with the tandem arranged genes GAL10 and GAL7, inefficient transcriptional termination of the upstream gene inhibits initiation of transcription on the downstream gene. We now show that transcriptional interference can occur also with S. cerevisiae RNA polymerase II genes arranged convergently. We demonstrate that when the GAL10 and GAL7 genes are rearranged in a convergent orientation, transcriptional initiation occurs at full levels. However, as soon as the two transcripts begin to overlap, elongation is restricted, resulting in a severe reduction in steady-state mRNA accumulation. This effect is observed only in cis arrangement, arguing against RNA-interference effects acting on the potential generation of antisense transcripts. These data reinforce the necessity of separating adjacent RNA polymerase II transcription units by efficient termination signals.

We identify Rpa12p of RNA polymerase I (Pol I) as a termination factor. Combined analyses using transcription run-on, electron microscopy-visualized chromatin spreading and RT-PCR have been applied to the rRNA-encoding genes of Saccharomyces cerevisiae. These confirm that Pol I termination occurs close to the Reb1p-dependent terminator in wild-type strains. However, deletion mutants for the 3 end-processing enzyme Rnt1p or the Rpa12p subunit of Pol I both show Pol I transcription in the spacer. For ⌬rpa12, these spacer polymerases are devoid of nascent transcripts, suggesting they are immediately degraded. The homology of Rpa12p to the small subunit Rpb9p of Pol II and Rpc11p of Pol III, both implicated in transcriptional termination, points to a common termination mechanism for all three classes of RNA polymerase.

Human Ishikawa endometrial cells form domes when confluent monolayers are stimulated with fresh fetal bovine serum. Extensive structural and biochemical changes have been detected during the approximately 30 h differentiation period. The earliest detectable change involves the formation of multinucleated structures and the appearance of "granules" that stain for biotin within those structures. Nuclei become associated with each other and are ultimately enclosed within a biotin-containing membrane. Aggregated membrane-sheathed nuclei and the cells containing them begin to elevate from the dish as biotin staining becomes apparent in apical membranes. The elevated structures are called predomes and consist of one or more very large cells containing the sheathed nuclei. Apical membranes of these unusual cells extend far out into the medium in structures that resemble endometrial pinopods. A lumen under the elevated cells fills with transcytosed fluid. As differentiation proceeds, highly concentrated chromatin material that was flattened against apical and lateral membranes of the predome cells begins to disperse. Small mononuclear cells evolve from larger predome cells. Apical membranes of predome and dome cells continue to stain for biotin. Gel electrophoresis of SDS-solubilized biotin-containing membranes, followed by Western blot analysis using avidin-linked peroxidase, resulted in three stained bands with molecular weights similar to those of the mitochondrial carboxylases: propionyl carboxylase, methylmalonyl carboxylase, and pyruvate carboxylase.

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