Further structural and functional analogies between the repressor regions of phages P22 and λ

Abstract

Mutants of P22 which have been located in the c2 repressor gene were examined. The most rightward "c2 mutation" was found to define a site that is necessary only for the establishment and not for the maintenance of repressor synthesis. We conclude that this site c27 is an analog of cy mutants in phage lambda which define a promotor for repression establishment (pre). The K5 mutation of P22 maps between c27 and all other c2 mutants. Examination of its biological behavior and direct measurement of repressor activity show that K5 does not affect c2 repression. A model to explain these findings implies that c27 and K5 affect transcripts of opposite directions. P22 c1 mutants do not allow c2 repressor synthesis and we conclude that the activity of c1 product (and presumably c3 product) at the site defined by c27 is necessary for repressor synthesis. The combined activity of c1 and c3 product at c27 is postulated to promote repressor synthesis and block transcription of vegatative phage genes to the right of K5. After repressor synthesis has been established, another site analogous to lambda prm is sufficient for repressor synthesis and c27 is no longer required. These observations and conclusions point to a very close analogy between repressor synthesis and control in phages P22 and lambda.

Identification and characterization of mutations in Escherichia coli that selectively influence the growth of hybrid lambda bacteriophages carrying the immunity region of bacteriophage P22

“…The hybrid representing the first class carries the c2-5 mutation, and the hybrid representing the second class carries the cy27 mutation. The former results in the synthesis of an inactive repressor protein, and the latter inactivates the PE promoter from which transcription of c2 is established (25 Quantitative experiments measuring the burst of phages in the Sip mutants confirm the qualitative experiments discussed above. The burst of the cl+ hybrid phages was reduced at least 2 orders of magnitude in the Sip mutants (Table 4).…”

“…Furthermore, in comparing the EOP of X immP22 c2-5 in the sipB391-nusAl strain with the EOP in the sipB391-nusE71 strain, we found a 300-fold reduction in the nusAI derivative. Note that there was no effect on the EOP in the nusAl and nusE71 derivatives of the Sip' parent of the sipB391 (25,48,55 (ii) Another cIl-activatible promoter, PaQ, is located in the Q gene and is positioned to transcribe toward PR (Fig. 8) (31 and 51).…”

“…Since one of the principle roles of cl is to initiate expression of the c2 (repressor) gene (25,35), we determined whether the c2 protein was ultimately involved in the Sipimposed block on the growth of A imm 22 by using hybrid phages with mutations that either result in an inactive c2 protein or block the transcription of the c2 gene. The hybrid representing the first class carries the c2-5 mutation, and the hybrid representing the second class carries the cy27 mutation.…”

“…However, we can conclude that the inhibition of phage growth in Sip mutants is not due to the action of repressor, the product of the c2 gene, because K imm 2. derivatives that are c2-fail to grow in Sip hosts, and both c2 and cI (encodes K repressor) mutants show normal cl and cII regulation of lytic gene expression (14,25).…”

Site c27 in phage P22 and control of the pathway to lysogeny

“…The bacterial and phage strains used in this work were described in Gough and Tokuno (1975) with the exception of PR-POX. MG3 is a wild type S. typhimurium.…”