In vivo analysis of the plasmid pAM beta 1 resolution system

Site-specific DNA Inversion by Serine Recombinases

Reversible site-specific DNA inversion reactions are widely distributed in bacteria and their viruses. They control a range of biological reactions that most often involve alterations of molecules on the surface of cells or phage. These programmed DNA rearrangements usually occur at a low frequency, thereby preadapting a small subset of the population to a change in environmental conditions, or in the case of phages, an expanded host range. A dedicated recombinase, sometimes with the aid of additional regulatory or DNA architectural proteins, catalyzes the inversion of DNA. RecA or other components of the general recombination-repair machinery are not involved. This chapter discusses site-specific DNA inversion reactions mediated by the serine recombinase family of enzymes and focuses on the extensively studied serine DNA invertases that are stringently controlled by the Fis-bound enhancer regulatory system. The first section summarizes biological features and general properties of inversion reactions by the Fis/enhancer-dependent serine invertases and the recently described serine DNA invertases in Bacteroides. Mechanistic studies of reactions catalyzed by the Hin and Gin invertases are then discussed in more depth, particularly with regards to recent advances in our understanding of the function of the Fis/enhancer regulatory system, the assembly of the active recombination complex (invertasome) containing the Fis/enhancer, and the process of DNA strand exchange by rotation of synapsed subunit pairs within the invertasome. The role of DNA topological forces that function in concert with the Fis/enhancer controlling element in specifying the overwhelming bias for DNA inversion over deletion and intermolecular recombination is emphasized.

Sin recombinase from Staphylococcus aureus: synaptic complex architecture and transposon targeting

The Sin recombinase from Staphylococcus aureus builds a distinctive DNA-protein synaptic complex to regulate strand exchange. Sin binds at two sites within an 86 basepair (bp) recombination site, resH. We propose that inverted motifs at the crossover site, and tandem motifs at the regulatory site, are recognized by structurally disparate Sin dimers. An essential architectural protein, Hbsu, binds at a discrete central site in resH. Positions of Hbsu-induced DNA deformation coincide with natural targets for Tn552 integration. Remarkably, Sin has the same topological selectivity as Tn3 and gammadelta resolvases. Our model for the recombination synapse has at its core an assembly of four Sin dimers; Hbsu plays an architectural role that is taken by two resolvase dimers in models of the Tn3/gammadelta synapse.

DNA cloning in Lactobacillus helveticus by the exconjugation of recombinant mob-containing plasmid constructs from strains of transformable lactic acid bacteria

A system developed for the genetic transfer of plasmids between strains of nontransformable bacteria (P. Langella, Y. le Loir, S. D. Ehrlich and A. Gruss, 1993, J. Bacteriol., 175, 5806-5813) by the specific inclusion of a mobilization (mob) region into a nonconjugative shuttle vector was used successfully to deliver the genetic determinants for beta-glucanase, beta-glucuronidase, and green fluorescent protein to Lactobacillus helveticus. Expression of two of the genes could be detected in the new host. Data suggested that resolution of cointegrates into components could release the original recombinant plasmid or generate a cointegrate deletion. All the recombinant plasmids were segregationally unstable in Lb. helveticus and there was some evidence for structural instability. Intrinsic instability in the mob-containing vector was reduced by replacing the duplicated pBluescript polylinker with that from pUC19. Sites at which cointegrate formation could occur were localized at two distinct tracts close to the D-loop that forms at the primosome during plasmid replication.

The L17 ribosomal protein of Bacillus subtilis binds preferentially to curved DNA

We searched in Bacillus subtilis for proteins that bind preferentially to curved DNA. Two proteins of 9 and 15 kDa displaying this property were purified from exponentially growing cells of B. subtilis strain 168. Sequencing of N-terminal amino acids identified them as the proteins HBsu and L17 respectively. The overproduction of L17 from B. subtilis in Escherichia coli was shown to have a strong effect on nucleoid morphology and segregation.

Comparative analysis of staphylococcal plasmids carrying three streptogramin-resistance genes: vat-vgb-vga

Several staphylococcal plasmids (26-45 kb) carry all three streptogramin-resistance (Sg(R)) genes, vat, vgb, and vga. Seven such plasmids harbored by independent strains belonging to three taxa (Staphylococcus aureus, S. simulans, and S. cohnii subsp. urealyticum) were compared and the deleted derivative of one of them, pIP680 (11.3 kb), carrying the three streptogramin-resistance genes was sequenced. The seven native plasmids had in common a 12.1-kb part cocarrying the three Sg(R) genes. Sequence analysis of pIP680 revealed that the simultaneous presence of these three genes has probably resulted from cointegration of two plasmids: (i) a pAMbeta1-like plasmid harboring vat-vgb and whose replication gene has been inactivated by an IS257 insertion and (ii) a functional vga plasmid whose replication is similar to that of two staphylococcal plasmids, pSX267 and pSK41.