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

Repetitive elements flanked by exons 2 and 3 of the human transaldolase gen e, thus termed transaldolase-associated repetitive elements, TARE, were ide ntified in human DNA, Nonpolyadenylated TARE transcripts were detected by N orthern blot analysis and cloned by reverse transcriptase-mediated polymera se chain reaction from human T lymphocytes, A dominant 1085-nucleotide long transcript, TARE-6, contained two adjacent Alu elements, a right monomer a nd a complete dimer, oriented opposite to the direction of transcription of the transaldolase gene. Reverse transcriptase-polymerase chain reaction an d in vitro transcription analyses showed that transcription of TARE-6 proce eded in the orientation of the RNA pol III promoter of the Alu dimer and op posite to the orientation of the TAL-H gene. TAREs lacking RNA polymerase I II promoter showed no transcriptional activity. In vitro transcription of T ARE-6 was resistant to 1 mu g/ml alpha-amanitin but sensitive to 100 mu g/m l alpha-amanitin and tagetitoxin, suggesting involvement of RNA polymerase III. TAREs in both the transaldolase and HSAG-1 genomic loci were surrounde d by TA target site duplications. Homologies between transaldolase and HSAG -1 break off internally at splice donor and acceptor sites. The results sug gest RNA polymerase III-mediated transcription of TARE may be a source of r epetitive elements, contributing to distinct genes and thus shaping the hum an genome.