DNA inversion regions Min of plasmid p15B and Cin of bacteriophage P1: evolution of bacteriophage tail fiber genes

Abstract

Plasmid pl5B and the genome of bacteriophage P1 are closely related, but their site-specific DNA inversion systems, Min and Cin, respectively, do not have strict structural homology. Rather, the complex Min system represents a substitution of a Cin-like system into an ancestral pl5B genome. The substituting sequences of both the min recombinase gene and the multiple invertible DNA segments of pl5B are, respectively, homologous to the pin recombinase gene and to part of the invertible DNA of the Pin system on the defective viral element e14 ofEscherichia coli K-12. To map the sites of this substitution, the DNA sequence of a segment adjacent to the invertible segment in the P1 genome was determined. This, together with already available sequence data, indicated that both P1 and pl5B had suffered various sequence acquisitions or deletions and sequence amplifications giving rise to mosaics of partially related repeated elements. Data base searches revealed segments of homology in the DNA inversion regions of pl5B, e14, and P1 and in tail fiber genes of phages Mu, T4, P2, and K. This result suggests that the evolution of phage tail fiber genes involves horizontal gene transfer and that the Min and Pin regions encode tail fiber genes. A functional test proved that the pl5B Min region carries a tail fiber operon and suggests that the alternative expression of six different gene variants by Min inversion offers extensive host range variation.Plasmid p15B is a P1 prophage-related resident of Escherichia coli 15T-(18). Electron microscopy heteroduplex studies revealed that approximately 82% of the 94-kb pl5B DNA hybridizes with the P1 genome (23). Since no phage particle with a P1-like morphology could be produced in E. coli 15T-(1, 18), pl5B DNA has been considered to be a defective prophage. One region of nonhomology between pl5B and P1 DNA covers the invertible segment of the P1 DNA (16, 23). Its corresponding region on pl5B carries a complex site-specific DNA inversion system called Min (17,34 Fig. 4).The complex Min system is closely related to simple DNA inversion systems which contain two crossover sites and constitute a two-state switch for gene expression: Cin of phage P1, Gin of phage Mu, Pin of the e14 element on E. coli K-12, and Hin of Salmonella typhimurium The crossover sites and recombinase genes of these systems are structurally homologous and can mutually substitute for their functions (for a review of these DNA inversion systems, called here the Din family, see reference 7; see also Fig. 4) The comparison of the DNA sequences of the pl5B Min region with previously determined sequences of the Cin region of phage P1 suggested that the invertible segment and part of the recombinase gene had been substituted by nonhomologous DNA on an ancestral pl5B genome (33). While one of the breakpoints from homologous to nonhomologous sequences had already been located within the recombinase genes, the second breakpoint remained undetermined because of incomplete P1 sequence data of this region.In this paper, the DNA ...

The pKO2 Linear Plasmid Prophage ofKlebsiella oxytoca

“…NC003995). Analyses of the tail fiber genes of other phages indicated that the horizontal transfer of sequence blocks within these genes is common (43,89). SDS-polyacrylamide gel electrophoresis of KO2 virions showed that a small number of very large protein molecules of about the size predicted for the gene 21 protein are present in virions but not in heads (Fig.…”

Genome of Bacteriophage P1

“…This extra region is partly identical to the N-terminal region of the tail fiber structural protein encoded by plasmid p15B, which has extensive regions of homology to P1 (268,269). The tail fiber genes of P1, p15B, and Mu appear to have evolved by exchange of segments within a common pool of tail fiber genes.…”

Acquisition and rearrangement of sequence motifs in the evolution of bacteriophage tail fibres

“…Conservation of amino acids among the D-type and among the G-type segments is not evenly distributed. Short regions of highly conserved residues are embedded in more variable regions (Haggard-Ljungquist et al, 1992;Sandmeier et ai, 1992). Both ends of the D-type as well as of the G-type segments, at which crossover sites are found, are among the most conserved regions.…”

“…The results of two studies on tail-fibre mosaics (HaggardIjungquist et ai, 1992;Sandmeier et at., 1992) are summarized in Fig. 1 and Table 1.…”