Zhang W et al. (2019) BMC Bioinformatics "PaSS: a sequencing simulator for PacBio sequencing."

Zhang W, Jia B, Wei C

[BMC Bioinformatics, 2019]

BACKGROUND: Third-generation sequencing platforms, such as PacBio sequencing, have been developed rapidly in recent years. PacBio sequencing generates much longer reads than the second-generation sequencing (or the next generation sequencing, NGS) technologies and it has unique sequencing error patterns. An effective read simulator is essential to evaluate and promote the development of new bioinformatics tools for PacBio sequencing data analysis. RESULTS: We developed a new PacBio Sequencing Simulator (PaSS). It can learn sequence patterns from PacBio sequencing data currently available. In addition to the distribution of read lengths and error rates, we included a context-specific sequencing error model. Compared to existing PacBio sequencing simulators such as PBSIM, LongISLND and NPBSS, PaSS performed better in many aspects. Assembly tests also suggest that reads simulated by PaSS are the most similar to experimental sequencing data. CONCLUSION: PaSS is an effective sequence simulator for PacBio sequencing. It will facilitate the evaluation and development of new analysis tools for the third-generation sequencing data.

Chissoe SL et al. (1997) Nucleic Acids Res "Representation of cloned genomic sequences in two sequencing vectors: correlation of DNA sequence and subclone distribution."

Chissoe SL, Marra MA, Hillier L, Wilson RK, Brinkman R, Waterston RH

[Nucleic Acids Res, 1997]

Representation of subcloned Caenorhabditis elegans and human DNA sequences in both M13 and pUC sequencing vectors was determined in the context of large scale genomic sequencing. In many cases, regions of subclone under-representation correlated with the occurrence of repeat sequences, and in some cases the under-representation was orientation specific. Factors which affected subclone representation included the nature and complexity of the repeat sequence, as well as the length of the repeat region. In some but not all cases, notable differences between the M13 and pUC subclone distributions existed. However, in all regions lacking one type of subclone (either M13 or pUC), an alternate subclone was identified in at least one orientation. This suggests that complementary use of M13 and pUC subclones would provide the most comprehensive subclone coverage of a given genomic sequence.

Cotter PJ et al. (2002) Bioinformatics "Improved database searches for orthologous sequences by conditioning on outgroup sequences."

Caffrey DR, Cotter PJ, Shields DC

[Bioinformatics, 2002]

MOTIVATION: Searches of biological sequence databases are usually focussed on distinguishing significant from random matches. However, the increasing abundance of related sequences on databases present a second challenge: to distinguish the evolutionarily most closely related sequences (often orthologues) from more distantly related homologues. This is particularly important when searching a database of partial sequences, where short orthologous sequences from a non-conserved region will score much more poorly than non-orthologous (outgroup) sequences from a conserved region. RESULTS: Such inferences are shown to be improved by conditioning the search results on the scores of an outgroup sequence. The log-odds score for each target sequence identified on the database has the log-odds score of the outgroup sequence subtracted from it. A test group of Caenorhabditis elegans kinase sequences and their identified C.elegans outgroups were searched against a test database of human Expressed Sequence Tag (EST) sequences, where the sets of true target sequences were known in advance. The outgroup conditioned method was shown to identify 58% more true positives ahead of the first false positive, compared to the straightforward search without an outgroup. A test dataset of 151 proteins drawn from the C.elegans genome, where the putative 'outgroup' was assigned automatically, similarly found 50% more true positives using outgroup conditioning. Thus, outgroup conditioning provides a means to improve the results of database searching with little increase in the search computation time.

Chan EY (2009) Methods Mol Biol "Next-generation sequencing methods: impact of sequencing accuracy on SNP discovery."

Chan EY

[Methods Mol Biol, 2009]

The advent of next-generation sequencing technologies has spurred remarkable progress in the field of genomics. Whereas traditional Sanger sequencing has yielded the first complete human genome sequence, next-generation methods have been able to resequence several human genomes. In this manner, next-generation approaches have powerful capabilities for understanding human variation. The throughput for these approaches is often measured in billions of base pairs per run, astounding numbers when compared with the millions of base pairs per day generated by automated capillary DNA sequencers. However, unlike traditional Sanger dideoxy sequencing, these methods have lower accuracy and shorter read lengths than the dideoxy gold standard. Are these limitations offset by the higher throughputs? An in-depth look at the single read and composite accuracy of these methods is presented. The stringent requirements for single nucleotide polymorphism (SNP) discovery utilizing these approaches is discussed along with a review of studies that have successfully employed next-generation sequencing methods for large-scale SNP discovery. Ultimately, the application of these ultra-high-throughput sequencing methods for SNP discovery will open up new horizons for understanding human genomic variation.

Warren RL et al. (2019) Bioinformatics "ntEdit: scalable genome sequence polishing."

Jaquish B, Isabel N, Jones SJM, Birol I, Zhang J, Bohlmann J, Mohamadi H, Bousquet J, Coombe L, Warren RL

[Bioinformatics, 2019]

MOTIVATION: In the modern genomics era, genome sequence assemblies are routine practice. However, depending on the methodology, resulting drafts may contain considerable base errors. Although utilities exist for genome base polishing, they work best with high read coverage and do not scale well. We developed ntEdit, a Bloom filter-based genome sequence editing utility that scales to large mammalian and conifer genomes. RESULTS: We first tested ntEdit and the state-of-the-art assembly improvement tools GATK, Pilon and Racon on controlled E. coli and C. elegans sequence data. Generally, ntEdit performs well at low sequence depths (<20X), fixing the majority (>97%) of base substitutions and indels, and its performance is largely constant with increased coverage. In all experiments conducted using a single CPU, the ntEdit pipeline executed in<14s and <3m, on average, on E. coli and C. elegans, respectively. We performed similar benchmarks on a sub-20X coverage human genome sequence dataset, inspecting accuracy and resource usage in editing chromosomes 1 and 21, and whole genome. ntEdit scaled linearly, executing in 30-40m on those sequences. We show how ntEdit ran in<2h20m to improve upon long and linked read human genome assemblies of NA12878, using high coverage (54X) Illumina sequence data from the same individual, fixing frame shifts in coding sequences. We also generated 17-fold coverage spruce sequence data from haploid sequence sources (seed megagametophyte), and used it to edit our pseudo haploid assemblies of the 20 Gbp interior and white spruce genomes in<4 and <5h, respectively, making roughly 50M edits at a (substitution+indel) rate of 0.0024. AVAILABILITY: https://github.com/bcgsc/ntedit. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Huang X-Y (1994) Computer Applications in the Biosciences "On global sequence alignment."

Huang X-Y

[Computer Applications in the Biosciences, 1994]

We present a dynamic programming algorithm for computing a best global alignment of two sequences. The proposed algorithm is robust in identifying any of several global relationships between two sequences. The algorithm delivers a best alignment of two sequences in linear space and quadratic time. We also describe a multiple alignment algorithm based on the pairwise algorithm. Both algorithms have been implemented as portable C programs. Experimental results indicate that for a commonly used set of gap penalties, the new programs produce more satisfactory alignments on sequences of various lengths than some existing pairwise and multiple programs based on the dynamic programming algorithm of Needleman and Wunsch.

Pierro G (2012) Adv Bioinformatics "Sequence Complexity of Chromosome 3 in Caenorhabditis elegans."

Pierro G

[Adv Bioinformatics, 2012]

The nucleotide sequences complexity in chromosome 3 of Caenorhabditis elegans (C. elegans) is studied. The complexity of these sequences is compared with some random sequences. Moreover, by using some parameters related to complexity such as fractal dimension and frequency, indicator matrix is given a first classification of sequences of C. elegans. In particular, the sequences with highest and lowest fractal value are singled out. It is shown that the intrinsic nature of the low fractal dimension sequences has many common features with the random sequences.

Katti MV et al. (2001) Mol Biol Evol "Differential distribution of simple sequence repeats in eukaryotic genome sequences."

Ranjekar PK, Gupta VS, Katti MV

[Mol Biol Evol, 2001]

Complete chromosome/genome sequences available from humans, Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana, and Saccharomyces cerevisiae were analyzed for the occurrence of mono-, di-, tri-, and tetranucleotide repeats. In all of the genomes studied, dinucleotide repeat stretches tended to be longer than other repeats. Additionally, tetranucleotide repeats in humans and trinucleotide repeats in Drosophila also seemed to be longer. Although the trends for different repeats are similar between different chromosomes within a genome, the density of repeats may vary between different chromosomes of the same species. The abundance or rarity of various di- and trinucleotide repeats in different genomes cannot be explained by nucleotide composition of a sequence or potential of repeated motifs to form alternative DNA structures. This suggests that in addition to nucleotide composition of repeat motifs, characteristic DNA replication/repair/recombination machinery might play an important role in the genesis of repeats. Moreover, analysis of complete genome coding DNA sequences of Drosophila, C. elegans, and yeast indicated that expansions of codon repeats corresponding to small hydrophilic amino acids are tolerated more, while strong selection pressures probably eliminate codon repeats encoding hydrophobic and basic amino acids. The locations and sequences of all of the repeat loci detected in genome sequences and coding DNA sequences are available at http://www.ncl-india.org/ssr and could be useful for further studies.

Craxton M (1993) Methods Mol Biol "Cosmid sequencing."

Craxton M

[Methods Mol Biol, 1993]

Howe KL (2019) Lab Anim (NY) "A new reference genome sequence for Caenorhabditis elegans?"

Howe KL

[Lab Anim (NY), 2019]