The rex region of bacteriophage lambda: two genes under three-way control

Abstract

The nucleotide sequence of the phage λ rex region consists of 1428 bp and codes for two genes, rex A and rexB. Hence the complete λ immunity region codes for four genes and covers 2664 bp of sequence unique to X, as defined by the left and right boundaries of the imm434 region. Coordinate expression of both rex A and rexB, which are co-regulated with the cI represser gene from promoters p rm and p re is responsible for the Rex phenotype i.e. exclusion of a wide variety of superinfecting phage such as T4rII. The position of a third promoter, p lit, which overlaps the carboxy-terminal end of the rex A coding region, permits expression of rexE without rexA, from the resulting 470 nucleotide lit RNA. The lit transcript, therefore, must act as messenger for rexE in the noncoordinate expression of the rexgenes that occurs late in λ lytic infection. The coordinate and noncoordinate expression of rexB and rex A suggests a dual role for the very hydrophobic rexE protein. Studies of λ early and late DNA replication implicate rexB as having auxiliary functions in both lysogenisation and lytic infection.