Laptenko O. Biochemical characterization of Thermus thermophilus transcription elongation factors GreA-1 and GreA-2. Spatial organization of RNA Polymerase complexes with Gre-factors.

Object of study: Transcription elongation bacterial factors: mechanism of action, and interaction with RNA Polimerase. Aim: To study the functional and structure specificities of Gre-gomologs from T. thermophilus and RNAP binary complex spatial organization. Methods used: photochemical, chromatographic, protein crystallography and radioisotope methods. Results, novelty: Crystal structure of T. thermophilus RNAP holoenzyme at 2,6 ? resolution has been solved. Unlike it's mesophilic counterparts T. thermophilus RNAP holoenzyme inactive at 37?C and requires thermal energy in order to stimulate open complex formation and initiation steps. The intrinsic cleavage activity of T. thermophilus RNAP increases in the range of pH 7,0-7,8. T. thermophilus Gre A-1 exhibits efficient transcript cleavage activity towards ternary elongation complex with specificity similar to that of E. coli Gre A (type "A" cleavage activity). It also stimulates formation of full-size RNA-transcript. Gre A-2, on the other hand, inhibits the cleavage activity of GreA-1 as well as intrinsic Gre-independent nucleolytic activity of T. thermophilus RNAP. In addition it appears to act as a general inhibitor of transcription process, affecting both the initiation and elongation stages. The interactions of E. coli RNAP with Gre-factors were characterized and ?? biocamically. Based on the results obtained we conclude that both Gre-factors (GreA and GreB) bind to RNAP near the opening of its "secondary channel" where ? are adjoined. The ?? subunit is the primary target for Gre binding. The N-terminal coiled-coil domain of the Gre-factors protrudes through RNAP "secondary channel" interacting with the extended coiled-coil domain of ?? subunit, the F-bridge helix (conserved region ??-F) and the G-loop (region ??-G).