Repression of ant synthesis early in the lytic cycle of phage P22

Abstract

Using SDS-polyacrylamide gel electrophoresis to study the early expression of P22 genes we show that early expression of the ant-gene (imm I region) is turned off after 6-8 min, independent of the 'late' acting mnt-repressor. A semi-clear mutant called cir5 is defective for this early ant turn-off. The mutation cir5 maps in the imm I region of P22 between genes mnt and ant. P22 cir5 mutants are defective for a repressor which acts in trans to regulate early ant synthesis. There appears to be no absolute requirement of the cir5 allele for the establishment of lysogeny. The overproduction of ant in the P22 cir5 mutant leads to a marked increase in abortive infections, killing the infected cells. The cir5-phenotype can be suppressed by an ant- mutation.

Clear plaque mutation sites linked to theimmIregion of the Salmonella phage P22

“…1) yields under the same conditions a fraction of 2 -4 x 10~2 turbid plaque formers by marker rescue from the prophage. This strongly suggests that the mutation in P22 cir4-l and in P22 cir6-l -like that of P22 dr5-\ (Harvey et al 1981) -maps outside the immC region. Preliminary deletion mapping (Harvey et al 1981) using lysogenic bacteria with partly deleted P22 prophages strongly suggested that the mutations map within or closely linked to the imml region.…”

“…The mutant P22 dr5-l (Harvey et al 1981) is defective in this early ant repression and exhibits only a low frequency of lysogenization as compared with P22 wild type. P22 cir5-l was one of several clear plaque isolates carrying a mutation mapping within or closely linked to the imml region of P22.…”

“…The three cir mutations complement each other and -with one possible exception -the cl, c2 and c3 mutations of the immC region. P22 cir6-l -like P22 cir5-l (Harvey et al 1981) -is suppressed by the ant~a,ml9 allele, whereas P22 cir4-l is not. The results are discussed in terms of the regulation of early ant expression.…”

“…Genes within the immC region regulate establishment and maintenance of lysogeny by the c2-repressor (Levine 1957; for review see Susskind & Botstein, 1978), whereas genes of the imml region regulate the expression of the antirepressor gene ant, which is an antagonist of the c2-repressor (Levine et al 1975;Botstein et al 1975;Susskind & Botstein, 1978). The expression of ant occurs very early after infection (Harvey, Heil & Prell, 1979;Harvey et al 1981) and is negatively regulated by two repressors, the products of genes cir5 (Harvey et al 1981; cir = control of immunity 1 region) and mnt (Gough, 1968). A defect in either of these regulatory products shifts the infection response predominantly (with P22 cir5~) or completely (with P22 mnt~) to lysis resulting in the formation of a more or less clear plaque in contrast to the turbid plaque formed by P22 wild type.…”

“…On the other hand the cir5-repressor is synthesized very early after infection before mnt-repression is established thus turning off ant expression after a short burst of synthesis from 3 to 6 min after phage infection (Harvey et al 1981).…”