Analysis of Bacteriophage P1 Immunity by Using X-P1 Recombinants
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Proc. Natl. Acad. Sci. USA Vol. 75, No. 11, pp. 5594-5598, November 1978 Genetics Analysis of bacteriophage P1 immunity by using X-P1 recombinants constructed in vitro (P1 repressor genes/PI antirepressor gene/PI dnaB analog gene/DNA cloning) NAT STERNBERG, STUART AUSTIN, DANIEL HAMILTON, AND MICHAEL YARMOLINSKY Cancer Biology Program, National Cancer Institute, Frederick Cancer Research Center, P.O. Box B, Frederick, Maryland 21701 Communicated by Gary Felsenfeld, August 10, 1978 ABSTRACT We describe the dissection and reconstruction MATERIALS AND METHODS of a complex control circuit, the P1 immunity system, by a method that involves inserting EcoRI-generated fragments of Bacterial and Phage Strains. The Escherichia coli strains P1 DNA into X vectors that can then be sequentially inserted used were NS985 (HfrH, sup+), RW842 [HfrH XA(int-FII)gajT] into a bacterial cell. Using these techniques we have isolated (14), YMC (supF) (15), K175 (supD, Xr) (10), Q1508 X-P1 hybrid phages that express the products of P1 genes cl, c4, [dnaB70(ts), thyAl (12), NS91 (C600 groPA15) (16), and N3072 ant, and ban and, in appropriately constructed lysogens, con- [HfrH, sup+, A (pro-lac) Xlii] (6). The X vector X firmed the roles played by the first three of these products in Dam15b538sr1X3c1857(ts)nin5 contains a single EcoRI site for phage immunity. In addition we have'localized to particular inserting EcoRI fragments of P1 DNA (11).' Hybrid phages P1 fragments the sites requisite for expression and repression obtained by inserting P1 fragments (11) are designated X-Pl:c4, of these gene products. The analysis leads to the conclusion that :cl gpant acts in trans to antagonize repression mediated by gpcl, X-Pl:c1, etc.; :c4 or refers to pertinent genes located on the in support of' one of two proposed models for gpant action. inserted P1 fragment. Other phages used were PlCm, Moreover, two features of the,immunity system are revealed: PlCmcl.100(ts), PlCmcl.55(am), PlCmc4.32, PlCmelrs, and (f) a hitherto unknown component that effects gpcl repression; Plvdrsban-l. Unless otherwise indicated, all of the P1 phages and (if) an unexpected ability of gpc4 to channel a superin- carried the Tn9 transposon (Cm). PlCmvirsant-10 and fecting cl'+ phage into the lysogenic state, which suggests that PlCmc4.32ant-17 were isolated from P1 lysogens made by gpc4 activity regulates the establishment phase of lysogeny. infecting strain NS985 with either PlCmvdrs or PlCmc4.32. The presence of the ant- mutation in these phages was con- Analysis of complex genetic'controls requires methods that firmed by their inability to make plaques on strain.K175(Plcry) permit parts of the control circuits to be isolated, characterized, (5). Mutational defects are indicated here by a minus sign su- and variously reassembled. We show here how the insertion of perscript unless an allele numbei is specified. defined DNA segments into X vectors that can be successively Media and Growth Conditions. Media and commonly used integrated into the chromosome of a suitable bacterium permits microbiological procedures for P1 and N were as described (13, the analysis of several interacting genes by reconstruction as 17). Because the attX-int region of the X vector has been re- well as dissection experiments. Because of the phenomenon of moved' by the b538 deletion (18), homologous recombination incompatibility, this type of analysis would not be possible if with the cryptic X prophage of 'strain RW842 was used to ly- the genes to be studied were located in a plasmid. sogenize with primary X-P1 hybrids. The subject of our analysis is the immunity to superinfection The experiments described in this report were carried out conferred by the plasmid prophage of coliphage Pl. This im- at an EKi-Pi containment level in accordance with the'stipu- munity is thought to' require the presence of two repressor lations specified in FCRC MUA# 1. proteins, the products of genes ci (1) and c4 (2) (gpcl and gpc4) Construction of Xatt+imm21-P1 and Xatt+imm434-P1 that are located in the separate immC and immI regions of the Hybrid Phages. The Xb538cI857(ts)nin5-P1 hybrids (X-P1 phage genetic map (Fig. 1). Gpcl represses the viral lytic hybrids) -were restructured first by recombination with functions. Gpc4 is thought to repress a second immI' gene, ant Xfmm21nin5 or Ximm434nin5 to replace the immX' region (or reb). The product of the ant gene has been postulated to act with'imm2l or imm434 and then by recombination with either in trans to antagonize gpcl-mediated repression (9) or Xb515b519Nam7cI857(ts) to replace the b538 deletion with in cis to replicate DNA of the superinfecting phage even in the the two smaller deletions, b515 and b519, which leave attX and presence of gpcl (i.e., it acts as a repressor bypass) (10). Phage the X int gene intact (18). The restructured hybrids (designated P7, which has a ci gene functionally identical to the ci gene Ximm2l-Pl or Ximm434-Pl) can lysogenize standard strains of P1 but differs from P1 in the specificity of its c4 repressor at 32 or 42°C. (9), is able to grow in a P1 lysogen because gpant of the in- Isolation of a X-P1:ban Hybrid. We took advantage of the fecting P7 phage is not repressed by gpc4 of the prophage. ability'of the P1 ban gene product to substitute for the dnaB and inter- protein of the host (12) in order to isolate a X-Pl:ban hybrid. We describe here the isolation, characterization, Strain Q1508(X) was infected with a pool of \-P1 hybrids (de- actions of individual X-P1 hybrids bearing EcoRI-generated rived from 1000 plaques). The infected cells were spread on fragments of P1 (11) that express each of the known components thymine-supplemented'Ll plates and incubated for 36 hr at of the P1 immunity system. An additional hybrid that'expresses 42°C. The frequency of infected cells that survived to form the P1 ban gene (12), known to be directly under cl control (13) colonies (3 X 10-6) was about 30-fold greater than the (Fig. 1), provides'an indicator of cl repression. dnaB70(ts) reversion frequency. Phage that formed turbid plaques at 320C and clear plaques at 42°C [phage with the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "ad- Abbreviations: Cm, chloramphenicol resistance transposon Tn9; am, vertisement" in accordance with 18 U. S. C. §1734 solely to indicate amber, ts, temperature sensitive; gpc4, gpcl, etc., gene product of gene this fact. c4, cl, etc. 5594 Downloaded by guest on September 27, 2021 Genetics: Sternberg et al. Proc. Natl. Acad. Sci. USA 75 (1978) 5595 2 1122 7 expresses should a riE n gpc4 lysogenization-deficient Plc4- I EoRI fragments r-,n i m permit phage to lysogenize. Of 50 independent RW842 (X-P1) lysogens Cm imml immC v virs screened, 2 showed a 100- to 1000-fold increase in the capacity l /~~~~~~~/\,'fl for being lysogenized by Plc4- (PlCmc4.32). The X-P1 phages gpf2 gpc4 gpant-.- gpban gpc1 (X-Pl:c4a and X-Pl:c4b) obtained from these lysogens were made att + int + and then integrated into another host (NS985). In NS985, as in the original host, they conferred proficiency to be lysogenized by Plc4.32 at high efficiency. Because 90-95% O1la ~ of the P1 phage recovered from the NS985 (X-Pl:c4, FIG. 1. P1 genome with the positions ofthe two immunity regions PlCmc4.32) lysogens still carried the c4.32 allele, lysogenization and the Cm (Tn9) transposon (3,4) above the bar and pertinent genes, by Plc4.32 was not due to recombination between the c4+ gene whose products are designated in the figure, below the bar. The extent of the X-P1 prophage and the c4- gene of the P1. (The re- of the deletions in the Plcry (5), Pldpro8a (6), and Pldprolla (6) maining 5-10% of the recovered P1 phage were Plc4+, by prophages are indicated by the black areas. The location of EcoRI- rescue of c4.32+ from the X-Pl:c4 prophages). Thus, the generated P1 fragments is based in part on the map of Bachi and Arber (7) and on our own marker rescue experiments using am X-Pl:c4 phages express gpc4 constitutively in the prophage state mutations (8). The virs mutation, located in the immI region (2, 9), and this product can act in trans to permit Plc4- to form stable permits the phage to express gpant constitutively even in the presence lysogens. of gpc4. Thus, when a P1 lysogen is infected with Plvirs, gpant is X-Pl:c4 Lysogens Are Immune to P1. Although expressed, repression of lytic functions is lifted, and the infecting Plcl.55(am) formed plaques efficiently and yielded a signif- phage grows. For the same reason, P7, whose ant gene expression is icant number of phage after infection of lysogens of either insensitive to repression by gpc4 of P1, will grow in a P1 lysogen. A-Pl:c4a or X-Pl:c4b, P1 wild type did not (Table 1, line 2). This immunity is probably a consequence of gpc4-mediated c1857(ts) allele] were isolated from these lysogens. Infection repression of the ant gene of the superinfecting phage, because with these phages (X-Pl:ban) increased by about 300-fold the PlIrs and P7, whose ant gene is not sensitive to repression by survival of Q1508(X) at 42°C. A Xatt +imm21-Pl:ban phage the gpc4 of P1, grew well in the X-Pl:c4 lysogens was constructed, and Q1508 lysogens containing this prophage (Table 1, line survived with unit efficiency at 42°C.