EXPRESSION OF SEA-URCHIN HISTONE GENES IN THE OOCYTE OF XENOPUS-LAEVIS

h22, the cloned repeat unit of Psammechinus miliaris histone genes, is transcribed and translated when injected into Xenopus oocyte nuclei. Transcription is mediated by polymerase B. RNAs indistinguishable from sea urchin histone messenger RNAs H2A and H2B are synthesized, but a large portion of transcripts is polydisperse. From hybridization experiments it can be deduced that the H2A and H2B messenger RNAs hybridize exclusively to the coding strand of the structural genes, whereas polydisperse RNA is homologous to both strands of the repeat unit. h22 transcripts are stable in the oocyte and direct the synthesis of sea urchin histone proteins H2A and H2B. h22 transcripts were isolated separately from oocyte nuclei and cytoplasm. The cytoplasmic RNA contained virtually all of the sea urchin H2A and H2B mRNAs, and some minor RNAs of discrete size. On the other hand, polydisperse RNA and RNA complementary to the antisense strand of h22 DNA remained in the nucleus. Covalent circularity of the h22 DNA seemed to be an important factor for the mode of transcription, since only circular h22 and circular pCRI-h22, but not linearized h22, produced H2B mRNA. These findings emphasize special, new aspects for both DNA transcription and RNA processing and transport within the living cell. © 1979.