IDENTIFICATION OF A BRASSICA-NAPUS CDNA CLONE ENCODING A PEPTIDE HIGHLY RELATED TO ABC10-BETA, THE SMALLEST AND COMMON SUBUNIT OF RNA-POLYMERASES OF SACCHAROMYCES-CEREVISIAE

Nuclear RNA polymerases, fundamental components of eukaryotic cells, a re multisubunit enzymes. While the structure and function of the RNA p olymerase subunits have been extensively studied in yeast and mammals, those of plant RNA polymerase subunits are largely unknown. Here we r eport the identification of a Brassica napus cDNA clone (pBRP10 beta) encoding a peptide (BRP10 beta) highly related to ABC10 beta, a 70 ami no acid peptide that is the smallest and common subunit of the three y east RNA polymerases and is essential for yeast cell viability. The de duced open reading frame of the clone is 216 bp long, encoding a 71-am ino acid peptide. The deduced peptide shows 78% similarity to the yeas t ABC10 beta and shows high similarities to other eukaryotic ABC10 bet a homologs as well. In addition, it contains a potential zinc-binding motif conserved in ABC10 beta homologs as well as in other subunits of RNA polymerases. Genomic DNA blot analysis suggests that this gene ma y constitute a gene family in B. napus. RNA gel blot a nalysis shows t hat a single band of transcript is detected in all major organs. Our f inding suggests that the RNA polymerases of B. napus may contain a pep tide subunit similar to the yeast ABC10 beta subunit.