Transcriptional properties of nucleoli isolated from Tetrahymena.

Nucleoli can be isolated from Tetrahymena in a yield of 30-60%. The isolated nucleoli contain rDNA (at least 90% pure) and have a protein to DNA ratio of 30:1. The endogenous RNA-polymerase activity of the r-chromatin has the following properties: (i) The in vitro transcript has a maximal size identical to the in vivo 35S rRNA precursor, demonstrating correct termination on the gene, (ii) 79% of the in vitro transcript is complementary to cDNA of 17S and 25S rRNA which is close to the theoretical maximum for the 35S rRNA precursor, (iii) the elongation rate of the endogenous RNA-polymerase molecules is 9-12 nucleotides/sec, (iv) an average of 4-16 active RNA polymerases are associated with each rDNA molecule depending upon the preparation.