Motif analysis

Version Compatibility

Reference examples tested with: HOMER 4.11+, MEME suite 5.5+ (STREME replaces DREME from 5.4+), monaLisa 1.10+, JASPAR 2024 CORE, HOCOMOCO v12, BioPython 1.83+, bedtools 2.31+.

DREME was removed from MEME suite 5.4+; use STREME instead. Some tutorials still reference DREME — verify the installed version via meme --version. JASPAR 2026 (released late 2025) integrates 1259 BPNet ChIP models in a Deep Learning collection; the CORE collection remains the standard PWM source.

Motif Analysis on ChIP-seq Peaks

"Find enriched DNA binding motifs in my ChIP-seq peaks" -> Discover de novo motif patterns and test for known TF motif enrichment in peak sequences, with appropriate background to control for compositional and positional biases.

• CLI (HOMER, fast): findMotifsGenome.pl peaks.bed hg38 outdir/ -size 200 -p 8
• CLI (MEME-ChIP, comprehensive): meme-chip -db JASPAR.meme peaks.fa
• R (regression-based, selective enrichment): monaLisa::calcBinnedMotifEnrR(seqs, bins, pwms)
• CLI (deep-learning-derived motifs): TF-MoDISco on BPNet attribution scores (see chip-deep-learning)

Motif discovery is sensitive to background choice and peak quality. Hyper-ChIPable artifacts at rRNA / housekeeping loci often produce false-positive motifs (GC-rich or A-T-rich biases of those regions). Filter peaks against blacklists and inspect peak distribution before running motif discovery.

Tool Taxonomy

Tool	Discovery type	Background handling	Strength	Fails when
HOMER findMotifsGenome.pl	De novo + known	GC-matched genomic regions (auto)	Fast (multi-core); integrated vertebrate/insect/plant DBs; one-command full report	Background can include unmasked repeats producing motif artifacts; -size given slow; auto background may include peaks themselves
MEME-ChIP	De novo (STREME, MEME) + central enrichment (CentriMo) + DB comparison (TOMTOM) + scanning (FIMO)	Markov order-2 from input; shuffled (preserves dinucleotide)	Comprehensive single command; rigorous statistics; HTML report	Slower; sequences must be 100-500 bp; central enrichment requires summit-centered peaks
STREME (MEME 5.4+)	De novo (replaced DREME)	Markov order-2	Bailey 2021 benchmark: more accurate than DREME/HOMER/MEME/Peak-motifs; handles 3-30 bp; scales to 100k+ sequences	Memory-hungry for very long sequences (>1 kb)
MEME (classical)	De novo (long, gapped)	Markov	Long motifs; gapped motifs	Slow (no parallel); replaced by STREME for short motifs
DREME	De novo (short)	Shuffled	Historical; small fast	Removed from MEME 5.4+; use STREME
monaLisa (Stadler lab)	Binned enrichment regression	Native (binned scoring)	Modern; regression-based; selectivity (TF-specific in differential peaks)	R-only; less integrated with browsers
AME (MEME suite)	Known motif differential	Matched background set required	Designed for two-set comparison (e.g., peaks vs. control regions)	Requires user-provided background set
CentriMo	Known motif central enrichment	Auto from input	Tests positional enrichment relative to peak center	Requires summit-centered peaks (200-500 bp)
FIMO	Motif scanning	Markov model	Genome-wide scanning at user-set p-value	Many false positives at p ≤ 1e-4; tighten to 1e-5 for whole-genome
HOMER scanMotifGenomeWide.pl	Motif scanning	None	Genome-wide scanning at fixed score threshold	Less calibrated than FIMO; HOMER's PWM format
RSAT peak-motifs	De novo + known	k-mer comparison	Web-server; multi-tool ensemble	Web limits; less reproducible from CLI
TF-MoDISco	DL attribution-based	Implicit in model	Motifs from BPNet/chromBPNet attribution scores; captures soft motif syntax	Requires trained DL model; see chip-deep-learning

Background Selection — The Biggest Source of Error

Motif enrichment p-values are conditional on the background distribution. Wrong background produces wrong motifs.

Background	What it preserves	Use case	Limitation
GC-matched genomic regions	Mononucleotide composition; chromatin context	TF motifs; avoid GC-bias artifacts	Doesn't preserve dinucleotide (CpG, TpA)
Dinucleotide-shuffled	CpG and TpA frequencies	Short motifs; avoiding repeat-derived artifacts	Doesn't capture genomic position context
Markov order-2 (trinucleotide)	Trinucleotide context	Compositional control; STREME/MEME default	Doesn't capture chromatin context
Peak-flanking sequences (±500 bp upstream/downstream of peak)	Local genomic context	When peak GC differs from genome	May contain shared regulatory motifs if peaks cluster
Repeat-masked input	Sequence with repeats replaced by N	Avoid TE-derived motif artifacts	Loses motifs in evolved-from-repeat regulatory elements
Input control peaks	Open-chromatin / artifact regions	TF discrimination from generic chromatin	Hard to obtain; controversial
Differential set (AME)	Treatment-condition-specific peaks vs ctrl peaks	Differential motif enrichment	Requires a control peak set

Practical default: STREME / MEME-ChIP with Markov order-2 (built-in default); HOMER with -mask flag (mask repeats); always inspect for repeat-derived motifs (e.g., Alu-derived AluY consensus, LINE motifs).

Window Around Summit Matters

Motif enrichment improves dramatically when sequences are summit-centered:

Window	When
±100 bp (200 bp total)	Sharp TFs (CTCF, p53); summit reliably reflects motif position
±150-250 bp (300-500 bp)	Most TFs and sharp histones; balance of motif coverage and noise
Full peak width (-size given)	Variable-width broad marks; computationally expensive
Whole gene body (>1 kb)	Almost always wrong; dilutes motif signal

For ChIP-seq broad histone marks (H3K27me3, H3K9me3) motif analysis is generally NOT informative — these marks reflect Polycomb / heterochromatin domains without sequence-specific binding. Motif analysis applies to TFs and to histone marks deposited by sequence-specific cofactors (H3K27ac partial, since BRD4 reads acetyl).

HOMER Workflow

# De novo + known motif discovery, repeat-masked, GC-matched background
findMotifsGenome.pl peaks.narrowPeak hg38 homer_out/ \
    -size 200 \
    -mask \
    -p 8

# With user-supplied background (e.g., control peaks or random genomic)
findMotifsGenome.pl peaks.narrowPeak hg38 homer_out/ \
    -size 200 -mask -p 8 \
    -bg background_peaks.bed

# Known motifs only (skip de novo; faster)
findMotifsGenome.pl peaks.narrowPeak hg38 homer_known_only/ \
    -size 200 -mask -nomotif

# Differential motif analysis: peaks gained in condition A vs condition B
findMotifsGenome.pl gained_in_A.bed hg38 differential_motifs/ \
    -size 200 -mask -bg gained_in_B.bed

HOMER output files:

• homerResults.html — de novo motifs ranked by significance
• knownResults.html — known motif enrichment
• homerMotifs.all.motifs — all de novo motifs (PWM format)
• knownResults.txt — tab-separated known motif stats

MEME-ChIP Workflow

# Center peaks to ±100 bp around summit (column 10 in narrowPeak)
awk 'BEGIN{OFS="\t"} {summit = $2 + $10; print $1, summit - 100, summit + 100, $4, $5, $6}' \
    peaks.narrowPeak > peaks_centered.bed
bedtools getfasta -fi hg38.fa -bed peaks_centered.bed -fo peaks_centered.fa

# Full MEME-ChIP analysis
meme-chip \
    -oc meme_chip_out/ \
    -db JASPAR2024_CORE_vertebrates_non-redundant_pfms_meme.txt \
    -meme-nmotifs 5 \
    -streme-nmotifs 10 \
    -minw 6 -maxw 20 \
    peaks_centered.fa

# MEME-ChIP runs: STREME (replaces DREME) + MEME + CentriMo + TOMTOM + FIMO
# CentriMo tests known motifs for central enrichment — strongest signal of
# direct binding vs. tethered/indirect binding

monaLisa Workflow (R, Regression-Based)

Goal: Test which TF motifs are enriched in specific bins of peaks (e.g., bins of differential log2FC, or bins of accessibility).

Approach: monaLisa builds a per-motif regression of peak signal on motif occurrence, controlling for GC content. Selective for TFs that discriminate between bins.

library(monaLisa)
library(JASPAR2024)
library(Biostrings)

# Load peaks and split into bins (e.g., quintiles of log2FC)
peaks <- rtracklayer::import('peaks.bed')
peaks$log2FC <- ...  # from differential analysis
bins <- bin(peaks$log2FC, binmode = 'equalN', nElement = 200)

# Get sequences around peak centers
seqs <- getSeq(BSgenome.Hsapiens.UCSC.hg38, resize(peaks, width = 500, fix = 'center'))

# Load JASPAR PWMs
pwms <- getMatrixSet(JASPAR2024, list(species = 9606, collection = 'CORE'))

# Compute binned motif enrichment with GC control
res <- calcBinnedMotifEnrR(seqs = seqs, bins = bins, pwmL = pwms, BPPARAM = MulticoreParam(8))

# Plot heatmap of motif enrichment vs bins
plotMotifHeatmaps(x = res, which.plots = c('log2enr', 'negLog10P'),
                   width = 1.8, maxEnr = 2, maxSig = 10)

Per-Tool Failure Modes

HOMER -- Background includes peaks themselves

Trigger: Running findMotifsGenome.pl without -bg on a large peak set covering >5% of genome.

Mechanism: HOMER auto-samples GC-matched genomic regions for background, which can overlap the peak set itself.

Symptom: Even known TF motif p-values are weak (>1e-3); de novo motifs less enriched than expected.

Fix: Supply explicit -bg background (e.g., random genomic intervals matching peak count and width) OR use MEME-ChIP with internal shuffled background.

HOMER / MEME -- Repeat-derived false-positive motifs

Trigger: Running on unmasked peaks; peaks cover transposable elements (Alu, LINE, LTR).

Mechanism: TEs contain over-represented k-mers that motif algorithms mistake for biology.

Symptom: Top de novo motif matches AluY consensus (~280 bp), LINE/L1, or LTR families.

Fix: Use -mask (HOMER) or pre-mask peak sequences with RepeatMasker; verify TOMTOM matches against legitimate TF databases.

STREME -- Memory failure on long sequences

Trigger: Running STREME on full-peak sequences (>1 kb each) with > 50k peaks.

Mechanism: STREME holds suffix structures in memory; long sequences explode RAM.

Fix: Resize peaks to ±100-250 bp summit-centered before STREME; or downsample peak count.

CentriMo -- No central enrichment due to wrong centering

Trigger: Using full peak coordinates (BED start, end) without recentering on summit.

Mechanism: Peak start coordinate is the left edge, not the summit; motif may be enriched near the summit but appears unenriched relative to the start.

Symptom: Known TF motifs show no central enrichment despite being clearly enriched overall.

Fix: Recenter sequences on summit: summit = start + summit_offset (narrowPeak column 10) before extracting FASTA.

FIMO -- Massive false positives at default p ≤ 1e-4

Trigger: Genome-wide scanning at FIMO default p-value threshold.

Mechanism: At p ≤ 1e-4, expect ~3M random matches in a 3 Gb genome; most are false positives.

Symptom: FIMO output has millions of motif "hits"; can't distinguish real binding.

Fix: Tighten to --thresh 1e-5 or stricter for genome-wide scans; or restrict scan to peaks: fimo --bgfile motif_bg motif.meme peaks.fa.

monaLisa -- GC bins not respected

Trigger: Running calcBinnedMotifEnrR without GC binning when peaks have systematic GC differences (e.g., promoters vs distal enhancers).

Mechanism: GC-rich motifs are over-enriched in GC-rich bins simply by chance.

Symptom: Top motifs are CpG-rich families (e.g., E2F, NRF1) regardless of biology.

Fix: Use background = 'genome' with GC-matched genomic background; or background = 'otherBins' with stratified GC.

Motif analysis on hyper-ChIPable regions

Trigger: Running motifs on peaks dominated by hyper-ChIPable artifacts (rRNA, tRNA, housekeeping).

Mechanism: These regions have systematic compositional biases (GC-rich, A-T-rich, repeat-derived); motifs from artifact peaks reflect compositional biology, not TF binding.

Symptom: Top de novo motif matches no known TF; high-GC or low-complexity consensus.

Fix: Apply blacklist + custom hyper-ChIPable filter (top-1% input signal) before motif analysis. See chipseq-qc.

Reconciliation: When Motif Methods Disagree

Pattern	Likely cause	Action
HOMER finds motif X; MEME-ChIP misses	Different background; HOMER may have permissive background	Run MEME-ChIP with explicit GC-matched background; check
MEME finds long gapped motif; STREME doesn't	MEME captures variable-length structure; STREME limited to 30 bp	Both are correct; report MEME for long motifs
Top de novo motif doesn't match TOMTOM databases	Novel motif OR repeat artifact OR compositional artifact	Inspect peaks for repeats; check input control; could be genuine novel TF
Known motif enriched but no de novo recovery	Insufficient enrichment for de novo; or motif is degenerate	Trust known motif enrichment; de novo needs strong signal
Differential motif gained in treatment but TF expression unchanged	TF post-translational regulation (binding mode change without expression change)	Check ChIP signal at known TF target genes; not a contradiction

Common Errors

Error / symptom	Cause	Solution
HOMER "configureHomer.pl genome not installed"	Genome not configured	perl configureHomer.pl -install hg38 (one-time)
MEME "sequence too short"	Peaks < motif min width	Resize peaks to ≥ 200 bp
MEME-ChIP "out of memory"	Too many long sequences	Resize peaks to ±100-250 bp; downsample
No enriched motifs	Peak quality / hyper-ChIPable / wrong background	Check FRiP, filter blacklist, supply explicit background
Top motif is GC-rich consensus	GC-bias in peaks not matched by background	GC-matched background (HOMER -bg or MEME shuffled with order-2)
FIMO produces millions of hits	p-value threshold too loose	--thresh 1e-5 for whole-genome; restrict to peaks for finer p
TOMTOM matches always say "no match"	Motif database species mismatch	Use vertebrates / insects / plants DB matching organism

References

• Heinz S et al 2010 Mol Cell 38:576 (HOMER)
• Bailey TL & Elkan C 1994 Proc ISMB (MEME)
• Bailey TL 2021 Bioinformatics 37:2834 (STREME)
• Machanick P & Bailey TL 2011 Bioinformatics 27:1696 (MEME-ChIP)
• Bailey TL et al 2015 Nucleic Acids Res 43:W39 (MEME suite update)
• Grant CE et al 2011 Bioinformatics 27:1017 (FIMO)
• Bailey TL & Machanick P 2012 Nucleic Acids Res 40:e128 (CentriMo)
• McLeay RC & Bailey TL 2010 BMC Bioinformatics 11:165 (AME)
• Machlab D et al 2022 Nucleic Acids Res 50:e49 (monaLisa)
• Castro-Mondragon JA et al 2022 Nucleic Acids Res 50:D165 (JASPAR 2022; CORE collection)
• Avsec Ž et al 2021 Nat Genet 53:354 (BPNet; soft motif syntax)
• Shrikumar A et al 2020 bioRxiv (TF-MoDISco)

Related Skills

• chip-seq/peak-calling - Upstream peak calling; recenter on summit for motif input
• chip-seq/chipseq-qc - Filter hyper-ChIPable artifacts before motif discovery
• chip-seq/chip-deep-learning - BPNet/chromBPNet for sequence-attribution motif discovery (TF-MoDISco)
• chip-seq/peak-annotation - Annotate peaks before motif discovery to filter promoters vs enhancers
• atac-seq/motif-deviation - chromVAR per-cell motif activity (ATAC-specific)
• atac-seq/footprinting - TOBIAS footprint analysis (ATAC; complementary to motif enrichment)
• sequence-manipulation/motif-search - General sequence motif scanning
• genome-intervals/proximity-operations - bedtools getfasta to extract peak sequences