An in vitro transcription system able to distinguish initiation at the 16-kDa promoter from elongation events was used to identify factors that might participate in transcription termination within oriC. Pausing in the oriC region occurs at the same sites where termination occurs in vivo. Ten of these sites overlap RNA:DNA junctions in oriC. The pausing that occurs in vitro was not converted to efficient termination by guanosine 5'-diphosphate 3'-diphosphate, NusA, and Rho alone or in

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... n, or by DnaA suggesting that in vivo other or additional factors contribute to termination at oriC. Transcription from the 16-kDa promoter was 90% inhibited by the nucleotides guanosine 5'-diphosphate 3'-diphosphate and guanosine 5'-triphosphate 3'-diphosphate in agreement with previous observations that this promoter is stringently regulated.