Using RepeatMasker to Identify Repetitive Elements in Genomic Sequences

RepeatMasker is a popular software tool widely used in computational genomics to identify, classify, and mask repetitive elements, including low-complexity sequences and interspersed repeats. RepeatMasker searches for repetitive sequence by aligning the input genome sequence against a library of known repeats, such as Repbase. Here, we describe two Basic Protocols that provide detailed guidelines on how to use RepeatMasker, either via the Web interface or command-line Unix/Linux system, to analyze repetitive elements in genomic sequences. Sequence comparisons in RepeatMasker are usually performed by the alignment program crossₘatch, which requires significant processing time for larger sequences. An Alternate Protocol describes how to reduce the processing time using an alternative alignment program, such as WU-BLAST. Further, the advantages, limitations, and known bugs of the software are discussed. Finally, guidelines for understanding the results are provided.