We report the isolation and nucleotide sequence (7878 bp) of a genomic clone encoding murine cytokeratin EndoB, a type-I intermediate filament protein that is expressed coordinately with EndoA in trophectoderm cells during blastocyst formation. This clone contains the complete endoB gene including the 5' upstream and 3' downstream flanking regions. Sequencing analysis reveals the endoB gene consists of seven exons and six introns. Although the positions of the six introns coincide exactly with those of other type-I cytokeratin genes, the endoB gene has lost the seventh intron, which resides in the sequences coding for tail domains of other type-I cytokeratins. The 5' upstream regions of endoA and endoB genes contain homologous sequences around the respective TATA-like boxes, suggesting their involvement in coordinate regulation of their transcription and/or post-transcription. Surprisingly, this clone contains at least four murine B l repetitive sequences. One typical B1 repetitive sequence was recognized in the 5' upstream region, and the other three in the 3' flanking region.
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