Sequences required for transcription termination at the intrinsic λtIterminator

Abstract

The λtI terminator is located approximately 280 bp beyond the λint gene, and it has a typical structure of an intrinsic terminator. To identify sequences required for λtI transcription termination a set of deletion mutants were generated, either from the 5′ or the 3′ end onto the λtI region. The termination efficiency was determined by measuring galactokinase (galK) levels by Northern blot assays and by in vitro transcription termination. The importance of the uridines and the stability of the stem structure in the termination were demonstrated. The nontranscribed DNA beyond the 3′ end also affects termination. Additionally, sequences upstream have a small effect on transcription termination. The in vivo RNA termination sites at λtI were determined by S1 mapping and were located at 8 different positions. Processing of transcripts from the 3′ end confirmed the importance of the hairpin stem in protection against exonuclease.