CRYSTAL-STRUCTURE OF THE GREA TRANSCRIPT CLEAVAGE FACTOR FROM ESCHERICHIA-COLI

TRANSCRIPTION elongation factors stimulate the activity of DNA-depende nt RNA polymerases by increasing the overall elongation rate and the c ompletion of RNA chains. One group of such factors, which includes Esc herichia coli GreA, GreB and eukaryotic SII (TFIIS), acts by inducing hydrolytic cleavage of the transcript within the RNA polymerase, follo wed by relase of the 3'-terminal fragment(1-5). Here we report the cry stal structure of GreA at 2.2 Angstrom resolution. The structure conta ins an amino-terminal domain consisting of an antiparallel alpha-helic al coiled-coil dimer which extends into solution, reminiscent of the c oiled coil in seryl-tRNA synthetases(6). A site near the tip of the co iled-coil 'finger' plays a direct role in the transcript cleavage reac tion by contacting the 3'-end of the transcript. The structure exhibit s an unusual asymmetric charge distribution which indicates the manner in which GreA interacts with the RNA polymerase elongation complex.