DNA-dependent RNA polymerase levels during the response of human peripheral lymphocytes to phytohemagglutinin.

The cellular levels of the various RNA polymerases have been monitored in resting human peripheral lymphocytes and in lymphocytes stimulated by phytohemagglutin. Activity was measured in the presence of exogenous templates following solubilization and chromatographic resolution of the different RNA polymerases. Resting lymphocytes contain Class I, II, and III RNA polymerases, although the respective levels of activity are very low compared to the levels in metabolically active cell types. During the PHA-induced transformation of resting lymphocytes, the Class I, II, and III enzyme levels rise dramatically. During four days exposure to PHA, the levels of RNA polymerases I and III (which synthesize, respectively, rRNA and the transfer and 5S RNAs) increase 17 fold, while the level of RNA polymerase II (which synthezies heterogeneous nuclear RNA) increase 8 fold. The possible relationship between enzyme levels and the regulation of gene expression is discussed.