In vivo transription termination efficiency and trans-acting anti-termination effect

Abstract

Bacteriophage T7 genome of 40 kb contains a terminator Tφ for the phage RNA polymerase, which is located between genes 10 and 11. These genes are only expressed by read-through at the terminator. Therefore, the in vivo termination efficiency of Tφ was measured. The results suggested that the entire sequence within a transcription unit affects in vivo termination efficiency, as it does in vitro efficiency [Lee, J. T., Kim, H., Moon, K., Kim, S., and Kang, C. (1991) Mol. Cells 1, 203-209]. However, the efficiency of transcription termination was higher in vivo than in vitro. Also the transcription products from pGEM3ZT reduced the in vivo termination efficiency of other transcription units by 10 to 20%-points in trans. This in vivo reduction, however, was less significant than the in vitro reduction (50%-points). Apparently, abortive initiation product RNAs from early transcribed region of pGEM3ZT are responsible for the in vivo trans-acting anti-termination effect, as they are for the in vitro effect reported previously [Lee, J. T., and Kang, C. (1992) Biochem. Int. 26, 163-170].