Human transaldolase-associated repetitive elements are transcribed by RNA polymerase III

Repetitive elements flanked by exons 2 and 3 of the human transaldolase gene, thus termed transaldolase-associated repetitive elements, TARE, were identified in human DNA. Nonpolyadenylated TARE transcripts were detected by Northern blot analysis and cloned by reverse transcriptase-mediated polymerase chain reaction from human T lymphocytes. A dominant 1085-nucleotide long transcript, TARE-6, contained two adjacent Alu elements, a right monomer and a complete dimer, oriented opposite to the direction of transcription of the transaldolase gene. Reverse transcriptase-polymerase chain reaction and in vitro transcription analyses showed that transcription of TARE-6 proceeded in the orientation of the RNA pol III promoter of the Alu dimer and opposite to the orientation of the TAL-H gene. TAREs lacking RNA polymerase III promoter showed no transcriptional activity. In vitro transcription of TARE-6 was resistant to 1 microg/ml alpha-amanitin but sensitive to 100 microg/ml alpha-amanitin and tagetitoxin, suggesting involvement of RNA polymerase III. TAREs in both the transaldolase and HSAG-1 genomic loci were surrounded by TA target site duplications. Homologies between transaldolase and HSAG-1 break off internally at splice donor and acceptor sites. The results suggest RNA polymerase III-mediated transcription of TARE may be a source of repetitive elements, contributing to distinct genes and thus shaping the human genome.