Intron sequences modulate feather keratin gene transcription in Xenopus oocytes.

We have shown that chicken feather keratin genes are transcribed at extremely low levels in Xenopus oocytes. Primer extension reactions using carefully selected primers have shown that none of the detectable transcripts are spliced. When the single intron, located in the 5' untranslated region, was removed from the gene, we observed a 5-fold increase in transcript initiation from the in vivo "cap" site. Significantly, this 5-fold increase was also observed when the feather keratin intron was replaced with a similar sized fragment from pBR322. We conclude that the efficiency of accurate transcriptional initiation of chicken feather keratin genes in the oocyte is affected by DNA sequences within the intron.