Regulation of transcription of mRNAs in mammalian cells plays a central role in growth and development, in abnormal growth such as cancer, and in infection and cellular transformation by viruses. Although there are important regulatory mechanisms that control the initiation of transcription in cells, it is increasingly apparent that transcription is also regulated closely at the level of RNA chain elongation and termination. Important genes and systems regulated in this manner include cellular oncogenes, histones, and growth of HIV and adenoviruses. Elongation complexes of RNA polymerase II with its DNA template and nascent transcript ("tenary complexes") are intermediates in the synthesis of all eukaryotic mRNAs. The passage of these complexes along the DNA template is controlled in part by specific signals that can cause the period before resuming, or to terminate and release its transcript, and in part by cellular factors that regulate the action of those genetic signals. This proposal describes studies of the elongation and termination properties of purified mammalian RNA polymerase II, with particular emphasis on defining the DNA/RNA signals that lead to transcription arrest and termination/release on elucidating the mechanism by which the enzyme elongates and terminates RNA chains, and the role of a transcriptional elongation factor, TFIIS, in modulating these processes. Specific aims of this proposal include (1) Characterization of RNA binding sites on the free polymerase that are implicated as central elements in the transcription elongation/termination process. (2) Structural analysis of ternary elongation complexes during normal elongation and at arrest/termination sites. (3) Identification and characterization of DNA sequences that determine transcription arrest and transcript release. (4) Structural and functional analysis of TFIIS, its interaction with RNA polymerase in ternary complexes, and its expression and activity in cells.