Transcription unit of the chicken histone H5 gene and mapping of H5 pre-mRNA sequences

We have analyzed the transcription unit of the gene coding for the erythrocyte-specific histone H5. RNA transcripts elongated in vitro by permeabilized immature cells hybridized to the template strand of the structural gene as well as to 3'-flanking sequences. Approximately 90% of the engaged RNA polymerase II molecules terminate transcription within a region of about 500 base pairs immediately downstream of the polyadenylation site. S1 nuclease protection experiments indicated that the downstream sequences are also transcribed in vivo, their relative amounts reflecting the distribution of RNA polymerases observed in vitro. RNA molecules extending up to 1.14 kilobase pairs downstream of the polyadenylation site were detected, but no unique site of termination was found. The sequence of the transcription termination region shows no obvious homology to those of other RNA polymerase II termination regions. The possible involvement of altered DNA and/or chromatin structures in the transcription termination process is discussed.