About Nullomers Database

The terms minimal absent words (MAWs) and nullomers both describe minimal-length oligomers absent from a genome or proteome. While nullomers are the shortest possible absent motifs in a species, the broader term MAW includes both nullomers and longer absent sequences which share a common characteristic: becoming present after removing either their leftmost or rightmost letter.

The Nullomers Database is a web-based resource which aims to provide an intuitive interface for sharing statistically significant non-occurring MAWs which are unexpectedly absent in several genomes and proteomes. This absence suggests negative selection. The provided results are significant absent genomic and peptide sequences as they have been assessed by Nullomers Assessor. Read more about the evaluation method or follow the step-by-step user quide to get more information on how to browse the interface.


If you use either Nullomers Assessor or data from Nullomers Database in your work, please cite the website URL and the publication:

Koulouras G, Frith MC. Significant non-existence of sequences in genomes and proteomes. Nucleic Acids Res. 2021;49(6):3139–3155.

Thank you!


For questions, suggestions, bug-reports, or feedback, please email us:

Grigorios Koulourasgkoulouras {at} gmail {dot} com
Martin Frithmcfrith {at} edu {dot} k {dot} u-tokyo {dot} ac {dot} jp


This work was supported by the Department of Information Technology and Human Factors, National Institute of Advanced Industrial Science and Technology.