Effects of repetitive and non-repetitive rat rDNA enhancer elements on in vivo transcription by RNA polymerases I and II.
Previous study has demonstrated that a far upstream 174-bp spacer sequence of the rat rRNA-encoding (rDNA) gene can function as an enhancer in vitro in an orientation- and distance-independent manner [Dixit et al., J. Biol. Chem. 262 (1987) 11616-11622]. To demonstrate that this element can also function in vivo, two rat rDNA-cat plasmids, one with the 174-bp element and the other without this sequence, were constructed and transfected into CHO cells. Primer extension analysis of the transcripts produced after transfection showed that transcription initiation occurred at the +1 site of the rDNA. The 174-bp sequence stimulated the rat polI promoter activity in cis 4-5-fold over the control (with the promoter alone). This RNA polymerase (polI) enhancer also stimulated the mouse metallothionein-I (MT-I) and SV40 promoter activities in vivo, irrespective of its distance and orientation. Further dissection of the 174-bp element revealed that the stimulatory activity on the RNA polymerase II (polII) promoter resides within the 37-bp and 43-bp domains at the 3' end of the 174-bp element. Unlike this spacer enhancer, the 130-bp repeat element (RE) proximal to the rat promoter [Ghosh et al., Gene 125 (1993) 217-222] was unable to modulate the polII promoter activity in vivo. These data show that while the non-repetitive enhancer sequence of rat rDNA is interchangeable for the polI and polII promoters, the RE is polI-specific.
Ghosh
A K
AK
Department of Pharmacology and Molecular Biology, Chicago Medical School, IL 60064.
Kermekchiev
M
M
Jacob
S T
ST
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D004275:DNA, Ribosomal; D004742:Enhancer Elements, Genetic; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D012318:RNA Polymerase I / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D051381:Rats; D012091:Repetitive Sequences, Nucleic Acid; D013539:Simian virus 40 / Q000235:genetics; D014158:Transcription, Genetic; D014162:Transfection
D004275:DNA, Ribosomal; D012319:RNA Polymerase II; D012318:RNA Polymerase I