Nucleic Acids Research, 1992, Vol. 20, No. 21 5713-5718
© 1992
MOLECULAR BIOLOGY |
Intramolecular triplex potential sequence within a gene down regulates its expression in vivo
1Molecular Biophysics Unit Bangalore 560 012, India 2Centre for Genetic Engineering, Indian Institute of Science Bangalore 560 012, India
* To whom correspondence should be addressed
Received July 15, 1992. Revised October 6, 1992. Accepted October 6, 1992.
Polypurine/polypyrimidine sequences have been shown to adopt intramolecular triple helix structures under torsional stress and/or at low pH. Such sequences have been observed within the the regulatory as well as the coding regions of several genes and the involvement of triple helical structure adopted by these sequences in transcriptional control has heen speculated. Taking advantage of codon degeneracy we have engineered a 38 bp long intramolecular triple helix potential polypurine/polypyrimidine sequence motif between the 37th and 50th codons of ß-galactosidase gene in the plasmid pBluescriptllSK + to investigate whether in vivo E.coli RNA polymerase would transcribe sequence motifs adopting triple helix structure, when present within the coding region of the gene. E.coli JM109 cells transformed with this construct pSBT1, exhibited 80% inhibition of ß-galactosidase expression compared to another construct pSBmT12 made using less preferred codons for identical amino acid sequence, but lacking the polypurine/polypyrimidine sequence motif. Truncated ß-galactosidase transcripts were observed for pSBT1 but not for pSBmT12. Here we report that a putative triple helix potential sequence within a gene can down regulate its expression by partially blocking the transcription elongation in vivo.
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