The promoters of the genes for colicin production, release and immunity in the ColA plasmid: effects of convergent transcription and Lex A protein

Abstract

The initiation sites of transcription in vivo for the three genes caa, cai and cal encoding respectively colicin A (Caa), the immunity protein (Cai) and the pColA lysis protein (Cal) have been analysed by nuclease S1 mapping. This analysis demonstrates that caa and cal form an operon. cai is located between these two genes and transcribed in the opposite direction from its own promoter. The start sites for caa and cai have also been determined in vitro. For caa, the same start site was found in vivo and in vitro. In contrast, for cai the most efficient start site in vitro was not used in vivo. LexA protein strongly repressed the in vivo and in vitro transcription of the caa-cal operon. As determined by DNase 1 protection experiments, LexA protein binds with a high affinity to an approximately 40 bp long sequence just downstream of the Pribnow box. The sequence of the binding site is composed of two overlapped "SOS boxes". Two transcripts of the caa-cal operon were detected by blot hybridization. The longer mRNA can direct the synthesis of both Caa and Cal while the shorter one is terminated at the end of caa. When the transcription of the caa-cal operon is induced, there is a strong interference with cai transcription.

Colicin Biology

“…Except for cloacin DF13, colicin operons con-tain two LexA boxes in tandem but overlapping by one or two bases (106,123,171,411,433,445,466,537,578,599,638,649). The two LexA boxes have been found in every colicin operon studied so far and in the same organization and location.…”

“…71,2007 COLICIN BIOLOGY 163 of the colicin (105,445). The minor mRNA is the largest one, as it corresponds to a transcript of the entire operon that is of both the colicin and the lysis genes for the pore-forming colicin operons and of the colicin, the immunity protein, and the lysis protein genes for the nuclease colicin operons (106,411,412,637). Thus, the lysis gene is transcribed at lower levels than the colicin gene.…”

Role of the carboxyl-terminal domain of TolA in protein import and integrity of the outer membrane

“…Restriction endonucleases and DNA-modifying enzymes were purchased from Boehringer Mannheim Biochemicals and Bethesda Research Laboratories. Colicins E2, E3, and A were prepared as culture supernatants of mitomycin-induced bacteria containing the requisite Col plasmids (4,18). Colicin El was prepared from DM1187 carrying pMY440 by carboxymethyl-Bio-Gel A column chromatography (28).…”

Convergent transcription initiates from oppositely oriented promoters within the 5' end regions of Drosophila melanogaster F elements.

“…Gene activity can be regulated through symmetric transcription by different mechanisms. RNA polymerase complexes travelling in opposite directions along a DNA duplex might encounter a considerable degree of steric hindrance, and reduced transcription because of interference of RNA polymerase progression has been indeed documented for adjacent genes organized in opposite and convergent orientations (12,23,34,43). Gene expression can be negatively regulated, via the formation of sense-antisense RNA hybrids, at the level of translation (36) as well as of nuclear export (22).…”