Organization of the immunity region immI of bacteriophage P1 and synthesis of the P1 antirepressor

Heisig, Anke; Riedel, H; Dobrinski, Beate; Schuster, Hans‐Uwe

doi:10.1016/0022-2836(89)90591-3

Cited by 23 publications

(40 citation statements)

References 35 publications

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“…Bacteria (with relevant markers) used were Escherichia coli JM83F' sup' Strr Tetr (12,31) and WM874 ara A(lac-pro) thi (original name, CSH26 [13]). Bacteria were grown in TY (19) or M9 (13) medium.…”

Section: Methodsmentioning

confidence: 99%

“…1) (8,25), the latter extending into P1 EcoRI fragment 25 (32). The numbering of bases follows the scheme outlined earlier (12). Relevant T7 RNA polymerase/promoter system for controlled expression of P1 immI proteins.…”

Section: Methodsmentioning

confidence: 99%

“…Heat induction of a Plc4ts lysogen causes bacterial filamentation (20). Filaments were also observed when antirepressor was synthesized from a multicopy plasmid (12). Therefore, it was suggested that inhibition of cell division is caused by the action of antirepressor.…”

Section: Methodsmentioning

confidence: 99%

“…A C1i Bof-controlled operator-promoter element, Op51-P5ia; a non-regulated promoter, P5lb; and the genes c4, icd (formerly called orfx), and ant are arranged in that order in clockwise orientation of the P1 map (1,8,12). The ant gene encodes two antirepressor proteins, Antl and Ant2, the latter initiating at an in-frame start codon (9,12). The product of the c4 repressor gene is a 77-base antisense RNA (4), acting on a target ant mRNA.…”

mentioning

confidence: 99%

“…The term icd (for interference with cell division) is used here to rename orfx. Therefore, the original antl6 mutant (24), which was later identified as an orfx mutation (12), is now called icd16.…”

mentioning

confidence: 99%

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Cloning, expression, and characterization of the icd gene in the immI operon of bacteriophage P1

1993

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The immI operon of P1 contains the genes c4, ied (formerly called orf), and ant which are constitutively transcribed in that order from a single promoter, PSib. C4 is an antisense RNA which is processed from the precursor transcript. C4 RNA acts as a translational repressor oficd, thereby also inhibiting antirepressor (ant) synthesis. We have cloned the icd and the overlapping icd and ant genes. We show, by means of plasmid deletion analysis, that icd is translationally coupled to ant. An internal in-frame deletion of icd making up 65% of the codons still allows antirepressor synthesis at a reduced rate, indicating that a functionally active icd gene product is dispensable for ant expression. We identify the product of the icd gene as a 7.3-kDa protein which interferes with cell division. The results suggest that constitutive expression oficd, in the absence of a functionally active antirepressor, prevents P1 lysogen formation because of its detrimental effect on the host cell.The temperate bacteriophage P1 is maintained as a unitcopy plasmid in the bacterial host. Maintenance of lysogeny requires the continuous expression of two genes, cl and c4, that code for repressors of lytic growth (for a review, see reference 33). The cl gene is located in the immunity region immC, and the C1 repressor acts on at least 14 operators (Ops) which are widely distributed over the P1 genome (2,5,6,29). The c4 gene is located in the immI region, and the C4 repressor prevents expression of the closely linked antirepressor gene ant (21). The antirepressor antagonizes the effect of the C1 repressor by an as yet unknown mechanism. A third regulatory gene, bof, encoding a corepressor of C1 is located in the immT region (18,28,30).A detailed analysis of the P1 immI operon revealed the following organization (see Fig. 1 and 2). A C1i Bof-controlled operator-promoter element, Op51-P5ia; a non-regulated promoter, P5lb; and the genes c4, icd (formerly called orfx), and ant are arranged in that order in clockwise orientation of the P1 map (1,8,12). The ant gene encodes two antirepressor proteins, Antl and Ant2, the latter initiating at an in-frame start codon (9, 12). The product of the c4 repressor gene is a 77-base antisense RNA (4), acting on a target ant mRNA. Interaction depends on the complementarity of two pairs of short sequences, a'-a2 and b'-b2, respectively. The sequences a' and b' are contained within loops of a stem-loop secondary structure of C4; that of a2 and b2 are contained in the target RNA and encompass the virs mutation and the ribosome-binding site of icd, respectively (3).

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Section: Methodsmentioning

confidence: 99%