Endogenization of ssDNA fragment from an infectious virus in the genome of the Chaetoceros tenuissimus

One of the smallest diatoms, Chaetoceros tenuissimus, maintains their population despite coexisting with infectious viruses during blooms. To further understand this relationship, here, we sequenced the C. tenuissimus NIES-3715 genome. A gene fragment of a replication-associated gene from its own infectious ssDNA virus (designated endogenous virus-like fragment, EVLF) was found to be integrated in a total of 41 Mbp of both haploid assemblies. In addition, the EVLF was transcriptionally active and conserved in nine other C. tenuissimus strains from different geographical areas, although the primary structures of their proteins varied. The phylogenetic tree further suggested that the EVLF was acquired by the ancestor of C. tenuissimus. A target site duplication, a hallmark for long interspersed nuclear element retrotransposons, flanked the EVLF. Therefore, the EVLF was likely integrated by a retrotransposon during viral infection. The present study used genome information provides further insights into the diatom-virus evolutionary relationship.

Functional Characterization of Tn4401, a Tn3-Based Transposon Involved inblaKPCGene Mobilization

ABSTRACTThe carbapenemase geneblaKPC, which is rapidly spreading worldwide, is located on a Tn3-based transposon, Tn4401. In a transposition-conjugation assay, Tn4401was able to mobilizeblaKPC-2gene at a frequency of 4.4 × 10−6/recipient cell. A 5-bp target site duplication was evidenced upon each insertion without target site specificity. This study demonstrated that Tn4401is an active transposon capable of mobilizingblaKPCgenes at high frequency.

Emergence of CTX-M-15-Producing Enterobacteria in Cameroon and Characterization of a blaCTX-M-15-Carrying Element

ABSTRACT CTX-M-15-producing Klebsiella pneumoniae and Escherichia coli emerged recently in Cameroon. CTX-M-15 was encoded by two different multiresistance plasmids, of which one carried an ISEcp1-bla CTX-M-15 element flanked by a 5-bp target site duplication and inserted within a Tn2-derived sequence. A truncated form of this element in the second plasmid was identified.

DNA Integration by Ty Integrase in yku70Mutant Saccharomyces cerevisiae Cells

ABSTRACT In the present work we examined nonhomologous integration of plasmid DNA in a yku70 mutant. Ten of 14 plasmids integrated as composite elements, including Ty sequences probably originating from erroneous strand-switching and/or priming events. Three additional plasmids integrated via Ty integrase without cointegrating Ty sequences, as inferred from 5-bp target site duplication and integration site preferences. Ty integrase-mediated integration of non-Ty DNA has never been observed in wild-type cells, although purified integrase is capable of using non-Ty DNA as a substrate in vitro. Hence our data implicate yKu70 as the cellular function preventing integrase from accepting non-Ty DNA as a substrate.

Evidence that chicken CR1 elements represent a novel family of retroposons.

We report the first precise delineation of a chicken CR1 element and show that it is flanked by a 6-base-pair target site duplication that occurred when this repetitive element transposed. The 3' end of this CR1 element is defined by an 8-base-pair imperfect direct repeat, and we infer that this sequence represents the 3' end of all intact CR1 elements. In contrast, the 5' ends are not unique, and we argue that this variation existed at the time each element transposed. We also provide evidence that CR1 elements transposed into preferred target sites. CR1 elements therefore appear to represent a novel class of passive retroposons.

Evidence that chicken CR1 elements represent a novel family of retroposons

We report the first precise delineation of a chicken CR1 element and show that it is flanked by a 6-base-pair target site duplication that occurred when this repetitive element transposed. The 3' end of this CR1 element is defined by an 8-base-pair imperfect direct repeat, and we infer that this sequence represents the 3' end of all intact CR1 elements. In contrast, the 5' ends are not unique, and we argue that this variation existed at the time each element transposed. We also provide evidence that CR1 elements transposed into preferred target sites. CR1 elements therefore appear to represent a novel class of passive retroposons.