TRANSCRIPTION TERMINATION AT THE ESCHERICHIA-COLI THRA TERMINATOR BY SPINACH CHLOROPLAST RNA-POLYMERASE IN-VITRO IS INFLUENCED BY DOWNSTREAM DNA-SEQUENCES
Lj. Chen et al., TRANSCRIPTION TERMINATION AT THE ESCHERICHIA-COLI THRA TERMINATOR BY SPINACH CHLOROPLAST RNA-POLYMERASE IN-VITRO IS INFLUENCED BY DOWNSTREAM DNA-SEQUENCES, Nucleic acids research, 23(22), 1995, pp. 4690-4697
We have investigated the mechanism of transcription termination in vit
ro by spinach chloroplast RNA polymerase using templates encoding vari
ants of the transcription-termination structure (attenuator) of the re
gulatory region of the threonine (thr) operon of Escherichia coil. Fou
rteen sequence variants located within its d(G+C) stem-loop and d(A+T)
-rich regions were studied. We found that the helix integrity in the s
tem-loop structure is necessary for termination but that its stability
is not directly correlated with termination efficiency. The sequence
of the G+C stem-loop itself also influences termination. Moreover, the
dA template stretch at the 3' end of the terminator plays a major rol
e in termination efficiency, but base pairing between the A and U trac
t of the transcript does not. From the studies using deletion variants
and a series of mutants that after the sequences immediately downstre
am from the transcription termination site, we found that termination
of transcription by spinach chloroplast RNA polymerase was also modula
ted by downstream DNA sequences in a sequence-specific manner. The sec
ond base immediately following the poly(T) tract is crucial for determ
ining the termination efficiency by chloroplast RNA polymerase, but no
t of the T7 or E. coli enzymes.