The region between DXS52 and Factor VIII gene in the human Xq28 chromosomal band contains a G+C-rich isochore to which many genes have been mapped. We report here the isolation and characterization of a transcript mapping about 50 kb telomeric from the vasopressin type 2 receptor gene in a 180-kb YACs/cosmid contig containing the L1CAM gene at its centromeric end. The determined transcribed sequence from a human fetal brain library is identical to that of the recently identified accessory protein HCFC1 (host cell factor, also called CI) that activates herpes simplex virus VP16 (αTIF) transactivator protein for association with the octamer motif-binding protein Oct-1 (Cell 74: 115, 1993). The gene is expressed in a ubiquitous pattern and a larger transcript of approximately 10 kb is present in all the tissues tested, while an alternatively spliced RNA of approximately 8.0 kb is present in muscle and heart tissues. Genomic sequencing allowed us to determine that the sequenced transcript is assembled from 26 exons spread over a relatively small genomic region of approximately 24 kb. This allowed us to determine that a previously reported cDNA clone arises from the splicing out of an internal portion of exon 8 which does not change the reading frame. All together these results raise the possibility that alternative mRNA processing could partly contribute to the diversity of the polypeptide HCFC1 family in a subset of tissues.
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