Purification and partial characterization of a transcription-inhibitory peptide from Tetrahymena

The protozoa Tetrahymena excretes a small peptide complex with an Mr of about 5,000. The peptide inhibits transcription by reducing the activity of the RNA polymerase. We have purified and partially characterized the peptide complex. It contains two peptide chains of apparent Mr 2,300 and 2,600, respectively. Magnesium ions in connection with the SH groups of cysteine play a role in holding together the two chains of the intact complex.