Preliminary study on the DNA-binding properties of phage ΦC31 integrase

Forty-nine metagenomic-assembled genomes from an aquatic virome expand Caudoviricetes by 45 potential new families and the newly uncovered Gossevirus of Bamfordvirae

Twenty complete genomes (29-63 kb) and 29 genomes with an estimated completeness of over 90 % (30-90 kb) were identified for novel dsDNA viruses in the Yangshan Harbor metavirome. These newly discovered viruses contribute to the expansion of viral taxonomy by introducing 46 potential new families. Except for one virus, all others belong to the class Caudoviricetes. The exception is a novel member of the recently characterized viral group known as Gossevirus. Fifteen viruses were predicted to be temperate. The predicted hosts for the viruses appear to be involved in various aspects of the nitrogen cycle, including nitrogen fixation, oxidation and denitrification. Two viruses were identified to have a host of Flavobacterium and Tepidimonas fonticaldi, respectively, by matching CRISPR spacers with viral protospacers. Our findings provide an overview for characterizing and identifying specific viruses from Yangshan Harbor. The Gossevirus-like virus uncovered emphasizes the need for further comprehensive isolation and investigation of polinton-like viruses.

Unusual site-specific DNA integration into the highly active pseudo-attB of the Streptomyces albus J1074 genome

The φC31-encoded recombination system has become a widely used tool for genetic analysis of streptomycetes, gene therapy and generation of transgenic animals. However, the application of this system, even in the context of its natural host genus, Streptomyces, may require a specific approach for each species. In this study, we have identified a novel pseudo-attB site, called pseB4, for integration of vectors using the φC31 system. More than 90 % of clones contained two copies of pSET152- or pOJ436-based cosmids, after their introduction into S. albus. The efficiency of the integration of φC31-based vectors into pseB4 is therefore comparable to that of the integration into attB. Moreover, in contrast with integration into the native attB, integration into pseB4 is not polar and does not require a complementary sequence in the TT-core region. Furthermore, an analysis of conjugation frequency revealed mutual inhibition of plasmid integration into either site when both the attB and pseB4 sites were present in the genome.