Plant 7SL RNA genes belong to type 4 of RNA polymerase III- dependent genes that are composed of mixed promoters
The genes transcribed by RNA polymerase III (pol III) display a great diversity in terms of promoter structure and are placed in four groups accordingly. Type 3 subset of pol III genes has promoter elements which reside entirely upstream of the coding region of the gene whereas type 4 consists of genes with mixed promoters that enclose intra- and extragenic regulatory sequences. Plant 7SL RNA genes have been previously classified as type 3 of pol III genes requiring an upstream sequence element and a canonical TATA box for transcriptional activity in transfected plant protoplasts. We have identified two novel functional control regions within the coding region of an Arabidopsis 7SL RNA gene (At7SL-1) that resemble tRNA gene-specific A and B boxes with respect to sequence and position. Single and multiple nucleotide substitutions in either of these regions resulted in a pronounced reduction of transcription activity in tobacco nuclear extract that was not caused by a decreased stability as shown by decay kinetics of wild type and mutant RNA transcripts. These findings suggest that plant 7SL RNA genes should be actually placed in type 4 of pol III-transcribed genes. As a consequence of substantially different upstream promoters utilized by plant and human pol III, in vitro transcription of 7SL RNA genes in heterologous systems is severely impaired. A chimeric human 7SL RNA gene that contains the 5′ flanking region up to position −300 of At7SL-1 is yet transcribed with a reduced efficiency in tobacco extract when compared with the plant wild-type gene, supporting the notion that internal regulatory elements contribute to full activity.
Document Type: Research Article
Affiliations: 1: Graduate School of Natural Sciences, Nagoya City University, Nagoya 467-8501, Japan, 2: Institut für Biochemie, Universität Würzburg, Biozentrum, Am Hubland, 97074 Würzburg, Germany, and 3: Institute of Plant Molecular Biology, Branišovska 31, 37005 Českě Budějovice, Czech Republic
Publication date: July 1, 2005