We analyzed the composition and abundance of two forms of RNA polymerase 11 (pol 11) holoenzyme in synchronized HeLa cells. We did not detect significant changes in pol 11 holoenzyme composition, but we noticed differences in the abundance of the two complexes at different stages of the cell cycle. Summarized data from several independent experiments demonstrate that pol 11 holoenzyme, which is purified by GST-TFIIS affinity chromatography, is more abundant during G1/S and S phases. Another form of pol 11 holoenzyme, which is purified by anti-CDK7 antibodies, shows relatively higher amounts in G2/M and early G1 phases. (C) 2003 Elsevier Science (USA). All rights reserved.