Transcriptional behavior of silkmoth chorion genes in vivo and in injected Xenopus laevis oocytes.

Abstract

A cloned fragment of Bombyx mori genomic DNA containing a pair of chorion genes was injected into Xenopus laevis oocytes. The RNA transcribed from the injected template was examined by primer extension analysis for the presence of transcripts initiated correctly from the two chorion genes. Using as primers a number of fragments derived from various parts of the injected DNA, we have found that transcription initiation around the cap sites of the chorion genes was considerably more frequent than that at other, seemingly random sites of the template. Injection of different quantities of template into the oocytes revealed that at high DNA concentrations, most transcripts were randomly initiated. However, when reduced amounts of DNA were injected into the oocytes, the extent of specific transcription increased dramatically while the proportion of nonspecific transcripts correspondingly decreased. The relative rates of specific initiation from the two chorion genes in injected oocytes resembled closely those observed in choriogenic follicles. Finally, the primer extension analysis revealed the presence of chorion antisense transcripts not only in injected oocytes but also in total RNA derived from follicular cells. The possible origin of these transcripts is discussed.