Sequencing of the Dutch elm disease fungus genome using the Roche/454 GS-FLX Titanium System in a comparison of multiple genomics core facilities.

As part of the DNA Sequencing Research Group of the Association of Biomolecular Resource Facilities, we have tested the reproducibility of the Roche/454 GS-FLX Titanium System at five core facilities. Experience with the Roche/454 system ranged from <10 to >340 sequencing runs performed. All participating sites were supplied with an aliquot of a common DNA preparation and were requested to conduct sequencing at a common loading condition. The evaluation of sequencing yield and accuracy metrics was assessed at a single site. The study was conducted using a laboratory strain of the Dutch elm disease fungus Ophiostoma novo-ulmi strain H327, an ascomycete, vegetatively haploid fungus with an estimated genome size of 30-50 Mb. We show that the Titanium System is reproducible, with some variation detected in loading conditions, sequencing yield, and homopolymer length accuracy. We demonstrate that reads shorter than the theoretical minimum length are of lower overall quality and not simply truncated reads. The O. novo-ulmi H327 genome assembly is 31.8 Mb and is comprised of eight chromosome-length linear scaffolds, a circular mitochondrial conti of 66.4 kb, and a putative 4.2-kb linear plasmid. We estimate that the nuclear genome encodes 8613 protein coding genes, and the mitochondrion encodes 15 genes and 26 tRNAs.

Identification of optimal protocols for sequencing difficult templates: results of the 2008 ABRF DNA Sequencing Research Group difficult template study 2008.

The 2008 ABRF DNA Sequencing Research Group (DSRG) difficult template sequencing study was designed to identify a general set of guidelines that would constitute the best approaches for sequencing difficult templates. This was a continuation of previous DSRG difficult template studies performed in 1996, 1997, and 2003. The distinguishing factors in the present study were the number of DNA templates used, the number of different types of difficult regions tested, and the inclusion of a follow-up phase of the study to identify optimal protocols for each type of difficult template. DNA templates with associated sequencing primers were distributed to participating laboratories and each laboratory returned their sequencing results along with descriptions of the experimental conditions used. The data were analyzed and the best protocols were identified for each difficult template. This information was subsequently distributed to the participating laboratories for a second round of sequencing to evaluate the general applicability of the optimized protocols. The average improvements in sequencing results were 11% overall, with a range of -25% to +43% using the optimized protocols. The full results from this study are presented here and they demonstrate that general experimental protocols and common additives can be used to improve the sequencing success for many difficult templates.

Strategies for genotyping: Effectiveness of tailing primers to increase accuracy in short tandem repeat determinations.

A problem associated with automated analysis of fluorescently labeled fragments separated by slab gel or capillary electrophoresis is the doublet peak formed when Taq DNA Polymerase adds a nontemplated nucleotide (generally an adenosine) to the 3' end of the product.This nontemplated addition (plus A) is primarily dependent on the 5' sequence of the reverse primer and, to a lesser extent, polymerase chain reaction (PCR) conditions. Primers may amplify the true product, the plus A product or a doublet product comprised of both. When using markers based on dinucleotide repeats, this single base pair difference can make binning and accurate automated analysis problematic. To drive the PCR reaction consistently to the plus A product, the sequence of the nonfluorescent primer used in amplification can be modified by adding a 5' tail favoring the nontemplated addition. The present study, conducted by the Fragment Analysis Research Group (FARG) of the Association of Biomolecular Resource Facilities, provided researchers with an opportunity to compare normal products amplified with a dinucleotide marker to products amplified with the same primer to which a 5' tail designed to promote the plus A product had been added. The study also included a sample amplified with a tetranucleotide repeat marker for comparison. The results from this study were returned to the FARG for comprehensive analysis and are reported here.