Combined Solution and Crystal Methods Reveal the Electrostatic Tethers That Provide a Flexible Platform for Replication Activities in the Bacteriophage T7 Replisome.

Recent structural studies of the bacteriophage T7 DNA replication system have shed light on how multiple proteins assemble to copy two antiparallel DNA strands. In T7, acidic C-terminal tails of both the primase-helicase and single-stranded DNA binding protein bind to two basic patches on the DNA polymerase to aid in replisome assembly, processivity, and coordinated DNA synthesis. Although these electrostatic interactions are essential for DNA replication, the molecular details for how these tails bind the polymerase are unknown. We have determined an X-ray crystal structure of the T7 DNA polymerase bound to both a primer/template DNA and a peptide that mimics the C-terminal tail of the primase-helicase. The structure reveals that the essential C-terminal phenylalanine of the tail binds to a hydrophobic pocket that is surrounded by positive charge on the surface of the polymerase. We show that alterations of polymerase residues that engage the tail lead to defects in viral replication. In the structure, we also observe dTTP bound in the exonuclease active site and stacked against tryptophan 160. Using both primer/extension assays and high-throughput sequencing, we show how mutations in the exonuclease active site lead to defects in mismatch repair and an increase in the level of mutagenesis of the T7 genome. Finally, using small-angle X-ray scattering, we provide the first solution structures of a complex between the single-stranded DNA binding protein and the DNA polymerase and show how a single-stranded DNA binding protein dimer engages both one and two copies of DNA polymerase.

Aedes pertinax, a Newly Recognized Mosquito Species in the United States.

Specimens of a mosquito new to the continental USA, Aedes pertinax, were retrospectively identified from 2 collections made in 2011 in Indian River County, FL. Routine mosquito surveillance in subsequent years yielded more than 700 specimens appearing in 100 collections. The distribution of this mosquito in Florida and the United States is currently unknown, and recognition of the adult female is likely hampered by morphological similarities to Ae. atlanticus and Ae. tormentor.

Differentiation of Aedes atlanticus and Aedes tormentor by restriction fragment length polymorphisms of the second internal transcribed spacer.

Using novel DNA sequence data, we designed a restriction enzyme assay that distinguishes Aedes atlanticus and Ae. tormentor, based on size polymorphisms. The restriction endonuclease Hpy188I digests polymerase chain reaction-amplified 2nd internal transcribed spacer products once for Ae. atlanticus and twice for Ae. tormentor, thus providing a useful method for identifying adult female collections that are generally considered morphologically indistinguishable.

Recovery of whole mitochondrial genome from compromised samples via multiplex PCR and massively parallel sequencing.

In forensic casework, compromised samples often possess limited or degraded nuclear DNA, rendering mitochondrial DNA a more feasible option for forensic DNA analyses. The emergence of massively parallel sequencing (MPS) has enabled the recovery of extensive sequence information from very low quantities of DNA. We have developed a multiplex PCR method that amplifies the complete mitochondrial genome in a range of forensically relevant samples including single cells, cremated remains, bone, maggot and hairs isolated from dust bunnies. Following library preparation, MPS yields complete or nearly complete mitochondrial genome coverage for all samples. To confirm concordance between sample types and between sequencing platforms, we compared sequencing results from hair and buccal swabs from two references. Low initial DNA input into the multiplex PCR allows for conservation of precious DNA while MPS maximizes recovery of genetic information.

Simultaneous detection of human mitochondrial DNA and nuclear-inserted mitochondrial-origin sequences (NumtS) using forensic mtDNA amplification strategies and pyrosequencing technology.

Next-generation sequencing technologies enable the identification of minor mitochondrial DNA variants with higher sensitivity than Sanger methods, allowing for enhanced identification of minor variants. In this study, mixtures of human mtDNA control region amplicons were subjected to pyrosequencing to determine the detection threshold of the Roche GS Junior(®) instrument (Roche Applied Science, Indianapolis, IN). In addition to expected variants, a set of reproducible variants was consistently found in reads from one particular amplicon. A BLASTn search of the variant sequence revealed identity to a segment of a 611-bp nuclear insertion of the mitochondrial control region (NumtS) spanning the primer-binding sites of this amplicon (Nature 1995;378:489). Primers (Hum Genet 2012;131:757; Hum Biol 1996;68:847) flanking the insertion were used to confirm the presence or absence of the NumtS in buccal DNA extracts from twenty donors. These results further our understanding of human mtDNA variation and are expected to have a positive impact on the interpretation of mtDNA profiles using deep-sequencing methods in casework.