SP6 RNA polymerase efficiently synthesizes RNA from short double-stranded DNA templates.

SP6 DNA-dependent RNA polymerase, like T7 RNA polymerase, can be used to synthesize RNA sequences from short DNA templates which contain the 18 base pair promoter region. Use of SP6 polymerase extends the range of possible 5' sequences of RNA products, since the preferred SP6 start site (of the RNA product) is 5'GAAGA, while T7 polymerase prefers 5'GGGAG. The SP6 start site can be advantageous in large-scale syntheses where high concentrations of RNA can lead to aggregation. Using the limited number of DNA templates described here, there appears to be a significant difference between the two enzymes: SP6 polymerase requires a complete duplex DNA substrate for efficient synthesis, unlike the T7 enzyme which works efficiently when only the 18 base promoter region is double-stranded. SP6 polymerase consistently produces higher yields of RNA than does T7 polymerase, and the reactions can be easily scaled up to produce milligram quantities of RNA.     

Maize chloroplast RNA polymerase: the 78-kilodalton polypeptide is encoded by the plastid rpoC1 gene.

The 180-, 120- and 38-kDa polypeptides found in highly purified maize plastid RNA polymerase preparations are encoded by the maize plastid genes rpoC2, rpoB, and rpoA, respectively [Hu, J. and Bogorad, L. (1990) Proc. Natl. Acad. Sci. USA. 87, pp. 1531-1535]. These genes have segments that specify amino acid sequences homologous to those of E. coli RNA polymerase subunits. The plastid gene products are designated b", b and a, respectively. We report here that the amino-terminal amino acid sequence of a 78-kDa polypeptide also found in highly purified maize plastid RNA polymerase preparations matches precisely the sequence deduced from the maize plastid rpoC1 gene which has segments homologous to the 5' end of the E. coli rpoC gene. Thus, the 78-kDa polypeptide is likely to be a functional component of maize plastid DNA-dependent RNA polymerase. This polypeptide is designated subunit b'. Three polypeptides unrelated to RNA polymerase have also been identified in this preparation.