Transcription of two classes of rat growth hormone gene-associated repetitive DNA: differences in activity and effects of tandem repeat structure.

The rat growth hormone (rGH) gene contains two classes of repetitive DNA arranged as clusters within intron B and the 3' flanking region. The major family is equivalent to the CHO type 2 DNA. The second ("truncated repeat", TR) is a truncated version of the first and occurs in certain neural-specific transcripts and genes ("identifier" elements, ID). Here we report, using the HeLa cell-free transcription assay, that RNA polymerase III (Pol III) efficiently initiates at internal promoters within a tandem array of rGH gene repetitive DNA monomers and results in a novel organization of overlapping Class III transcription units. Transcription competition studies revealed that the rat type 2 structures share Pol III transcription factors with a tRNA gene, a human Alu repeat, and a mutant VA1 gene. Also, the rGH type 2 but not the TR DNA efficiently promotes Pol III initiation, yet other TR members, which differ only in flanking DNA, are transcribed. Thus, the rGH gene is strikingly enriched with 10 repetitive DNA monomers; multimeric type 2 elements are actively transcribed; rGH-TR sequences are expressed only as part of larger transcripts promoted by type 2 DNA; and, type 2 DNA uses tRNA gene transcription factors. These studies show that flanking sequences, promoter organization and factor competition may all affect rat repetitive DNA expression.