An inhibitory effect of RGD peptide on protein-priming reaction of bacteriophages phi 29 and M2

The RGD sequence in phage phi29 terminal protein is required for interaction with phi29 DNA polymerase

The RGD (Arg-Gly-Asp) motif functions as a recognition site for adhesive proteins responsible for a number of cell-cell interactions. Certain viruses use this sequence as a receptor-binding site by interaction with cellular integrins. To elucidate the role of the RGD sequence of the phi29 terminal protein (TP), seven modified TPs were generated by site-directed mutagenesis. Most of the TP mutants were not efficiently used as primers, leading to a reduction of the TP-dAMP complex formation in the presence of the phi29 TP-DNA template. Moreover, these mutant TPs were poorly deoxyadenylylated by phi29 DNA polymerase in the absence of template. Analysis of primer TP/DNA polymerase complex formation showed that the modified TPs were affected in the formation of the heterodimeric complex. These results indicate that the RGD sequence present in phi29 TP is primarily involved in interaction with the viral DNA polymerase.

Plasmids containing cos ends inhibit the replication of phage phi CTX in Pseudomonas aeruginosa

In bacteriophage phi CTX, the cohesive end sequences cos, the integrase gene int, the attachment site attP (the target site for int) and the gene ctx encoding a pore-forming cytotoxin CTX, are clustered. Phi CTX can infect some Pseudomonas aeruginosa strains with a subsequent induction of CTX expression. The 41 and 477 bp fragments containing cos ends of phi CTX DNA were cloned into the high copy number plasmid pHA10. After pretransformation with the cos ends containing plasmids, plaque formation of phi CTX and cytotoxin production in phi CTX-infected Pseudomonas aeruginosa cells decreased by 100- and 10-fold respectively. Twelve hours after phi CTX infection proteins binding with cooperativity to cos sequence containing cleavable ends and the 10 bp flanking sequences were detected by gel electrophoretic mobility retardation of [32P]cos DNA. The results suggest that the cos binding proteins of phi CTX are involved in phi CTX replication.

Complementation assay of primer protein: gene expression systems of plasmid vectors support the infection of suppressor sensitive mutant phages M2 and phi 29

Two different expression systems of genes of primer proteins (pE for phage M2, and p3 for phi 29) were constructed to study the protein primed DNA replication of Bacillus phages M2 and phi 29. In one system, expression of the genes was under the control of the inducible spac promoter, whereas in the other system, the expression was under the control of the constitutive promoter in plasmid pUB110. Complementation tests in vivo were performed between the primer proteins expressed by these systems and mutant phages having suppressor sensitive mutations in the genes of the primer proteins. The phages M2 susE and phi 29 sus3 were complemented by pE and p3 expressed by the systems, respectively. However, the complementation and apparent phage DNA synthesis were not detected in the combinations between susE of phage M2 and p3 of phage phi 29, and vice versa. Although pE and p3 proteins exhibited structurally and functionally similar characteristics, these proteins showed species specificity in the protein primed DNA replication of bacteriophages M2 and phi 29.

Receptor sequence in the terminal protein of bacteriophage M2 that interacts with an RGD (Arg-Gly-Asp) sequence of the primer protein

At the initiation of protein-primed DNA replication of bacteriophages M2 and phi 29, the Arg-Gly-Asp (RGD) sequence of primer protein participates in the recognition of terminal protein (TP), where the initiation site for protein-primed DNA replication of template DNA is located. We compared the sequences of M2 and phi 29 TP with those of the members of the integrin superfamily and found the highly homologous sequences Lys-Lys-Ile-Pro-Pro-Asp-Asp (KKIPPDD) in M2 and phi 29 TP and Lys-Lys-Gly-Cys-Pro-Pro-Asp-Asp (KKGCPPDD) in the beta-subunit of fibronectin receptor protein. A synthetic 20mer peptide that contained the KKIPPDD sequence interfered with the inhibitory effect of the RGD peptide on both transfection and the protein-priming reaction in vitro. We propose that the sequence KKIPPDD of M2 TP is the receptor sequence for RGD.

Primer protein of bacteriophage M2 exposes the RGD receptor site upon linking the first deoxynucleotide

Primer protein (PP) of bacteriophages M2 and phi 29 contains an Arg-Gly-Asp (RGD) sequence. The RGD-mediated protein-protein interaction in protein-primed DNA replication of M2 was studied in vitro using three purified and indispensable components: PP, DNA polymerase (POL) and template DNA linked to terminal protein (TP). PP competed with a synthetic RGD peptide for binding to the template DNA-TP complex (TP-DNA). In addition, POL bound to template TP-DNA only when complexed with PP. These results indicate that the RGD sequence of PP is responsible for the interaction of the PP-POL complex with TP-DNA, which contains the initiation site for the protein priming of DNA synthesis. At the moment when PP converts to TP upon linking the first deoxynucleotide, a conformational change results in exposure of the RGD binding site.

The role of a stress-response protein in Salmonella typhimurium virulence

We recently described the use of selective transposon mutagenesis to generate a series of avirulent mutants of a pathogenic strain of Salmonella typhimurium. Cloning and sequencing of the insertion sites from two of these mutants reveals that both have identical locations within an open reading frame that is highly homologous to a gene, htrA, encoding a heat-shock protein in Escherichia coli. DNA sequence analysis of S. typhimurium htrA reveals the presence of a gene capable of encoding a protein with a calculated Mr of 49316 that has 88.7% protein:protein homology with its E. coli counterpart. In E. coli, lesions in this gene, also known as degP, reduce proteolytic degradation of aberrant periplasmic proteins. Characteristics of the S. typhimurium htrA mutants, 046 and 014, in vivo and in vitro suggested that they are avirulent because of impaired ability to survive and/or replicate in host tissues. In vitro, the S. typhimurium htrA mutants 046 and 014 are not temperature-sensitive but were found to be more susceptible to oxidative stress than the parent, suggesting that they may be less able to withstand oxidative killing within macrophages.