Elongin from Saccharomyces cerevisiae

Elongin is a transcription elongation factor that was first identified in m ammalian systems and is composed of the three subunits, elongin A, B, and C . Sequence homologues of elongin A and elongin C, but not elongin B, were i dentified in the yeast genome. Neither yeast elongin A nor C sequence homol ogues was required for cell viability. The two gene products could be purif ied from yeast as a complex. A recombinant form of the complex, which could only be produced in bacteria if the gene products were co-expressed, was p urified over several chromatographic steps. The complex did not stimulate t ranscription elongation by yeast RNA polymerase II. Using limited proteolys is, the N-terminal 144 residues of yeast elongin A were shown to be suffici ent for interaction with yeast elongin C, The purified complex of yeast elo ngin C/elongin A(1-143) was analyzed using circular dichroism and nuclear m agnetic spectroscopy. These studies revealed that yeast elongin A is unfold ed but undergoes a dramatic modification of its structure in the presence o f elongin C, and that elongin C forms a stable dimer in the absence of elon gin A.