COPE: an accurate k-mer-based pair-end reads connection tool to facilitate genome assembly

Bioinformatics. 2012 Nov 15;28(22):2870-4. doi: 10.1093/bioinformatics/bts563. Epub 2012 Oct 8.


Motivation: The boost of next-generation sequencing technologies provides us with an unprecedented opportunity for elucidating genetic mysteries, yet the short-read length hinders us from better assembling the genome from scratch. New protocols now exist that can generate overlapping pair-end reads. By joining the 3' ends of each read pair, one is able to construct longer reads for assembling. However, effectively joining two overlapped pair-end reads remains a challenging task.

Result: In this article, we present an efficient tool called Connecting Overlapped Pair-End (COPE) reads, to connect overlapping pair-end reads using k-mer frequencies. We evaluated our tool on 30× simulated pair-end reads from Arabidopsis thaliana with 1% base error. COPE connected over 99% of reads with 98.8% accuracy, which is, respectively, 10 and 2% higher than the recently published tool FLASH. When COPE is applied to real reads for genome assembly, the resulting contigs are found to have fewer errors and give a 14-fold improvement in the N50 measurement when compared with the contigs produced using unconnected reads.

Availability and implementation: COPE is implemented in C++ and is freely available as open-source code at

Contact: or

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms*
  • Arabidopsis / genetics*
  • Chromosome Mapping*
  • Contig Mapping
  • Genomics / methods*
  • Sequence Analysis, DNA / methods*