What types of RNA can CRACI-Seq detect dihydrouridine in?

CRACI-Seq detects D modifications across the whole transcriptome. It provides robust detection in tRNAs (cytoplasmic and mitochondrial) — where D is most abundant at canonical D-loop positions (D16, D17, D20, D20a, D20b, D47). It also supports exploratory detection of D sites in mRNA transcripts, though mRNA D sites are rare and typically low-stoichiometry (10–40%).

How does CRACI-Seq achieve quantitative stoichiometry?

The frequency of T→C misincorporation at a given position directly correlates with the fraction of RNA molecules carrying D at that site. HIV RT incorporates cytosine opposite reduced D with ~96% efficiency, and background correction using untreated (no KBH₄) control samples removes systematic noise. The resulting background-subtracted T→C fraction provides a direct readout of D stoichiometry at each site.

What makes CRACI-Seq better than D-seq or Rho-seq?

D-seq and Rho-seq rely on RT truncation, which has three limitations: (1) truncation efficiency does not correlate with modification fraction, precluding quantitative stoichiometry; (2) the first D site in a cluster blocks detection of downstream sites; (3) low truncation efficiency at certain sequence contexts causes false negatives. CRACI-Seq uses an internal misincorporation signal for quantitative, independent readout of each D position.

Can CRACI-Seq detect D in mitochondrial tRNAs?

Yes. CRACI-Seq has been validated for mitochondrial tRNA D detection, identifying D sites in mt-tRNAAsn, mt-tRNAGln, and mt-tRNALeu(UUR) — including moderate-stoichiometry sites (<40%) that are below the detection limit of truncation-based methods.

What sample types and quality are required?

We recommend ≥1 μg of high-quality total RNA (RIN ≥ 7) for standard CRACI-Seq. Small RNA enriched fractions (≥200 ng) are also suitable. Supported species include human, mouse, rat, and Arabidopsis. Untreated (no KBH₄) control samples are required for background modeling.

Quantitative RNA Dihydrouridine Mapping Service (CRACI-Seq)

What CRACI-Seq Measures

Dihydrouridine (D) is a unique RNA modification formed by the saturation of the uridine base — converting the C5–C6 double bond to a single bond. This reduction disrupts base-stacking and increases RNA backbone flexibility, playing critical roles in tRNA structural dynamics, codon recognition fidelity, and translation efficiency. D is catalyzed by four dedicated DUS writer enzymes (DUS1L–DUS4L), each targeting specific positions within tRNA D-loops, but the lack of quantitative mapping tools has limited functional studies of this modification.

CRACI-Seq (Chemical Reduction Assisted Cytosine Incorporation sequencing) uses a mild KBH₄ reduction to convert D to tetrahydrouridine, which instructs HIV reverse transcriptase — under an optimized high dGTP/dNTP ratio — to incorporate a cytosine opposite the reduced site. This produces a distinctive T→C misincorporation signature in the sequencing read, enabling single-base-resolution detection and quantitative stoichiometry assessment across the transcriptome.

Our service delivers comprehensive D modification analysis including: tRNA D profiling — accurate stoichiometry at all known D-loop positions (D16, D17, D20, D20a/b, D47) across cytoplasmic and mitochondrial tRNAs; DUS writer assignment — deciphering which enzyme modifies each site through perturbation designs; mitochondrial tRNA D analysis — detection of low-stoichiometry D sites in mt-tRNAs; and exploratory mRNA D discovery — identification of high-confidence D sites in protein-coding transcripts. We also offer tRNA Modification Analysis by LC-MS/MS as an orthogonal validation option for D site stoichiometry confirmation.

For researchers already working on broader epitranscriptome profiling, our Epitranscriptomics portfolio provides complementary services including Pseudouridine Sequencing (Pseudo-seq) for simultaneous analysis of multiple RNA modification types.

Feature	D-seq	Rho-seq / AlkAniline-Seq	CRACI-Seq (Our Service)
Detection principle	RT truncation at D sites (premature termination)	Chemical cleavage (AlkAniline) or RT stop (Rho-seq) at modified sites	Internal T→C misincorporation — HIV RT reads through reduced D, incorporates C opposite the site
Resolution	Single-base (indirect, via truncation boundaries)	Single-base (AlkAniline) or ~3–5 nt (Rho-seq)	Single-base — direct readout from misincorporation position
Quantitative stoichiometry	No — truncation efficiency does not correlate with modification fraction	Limited — AlkAniline cleavage efficiency varies by sequence context	Yes — T→C read fraction provides direct stoichiometry measurement with background correction
Clustered D sites (e.g., D16/D17 adjacent)	Poor — truncation at first D masks downstream sites	Poor — first site masks subsequent sites	Excellent — each site independently read out, enabling co-occurrence analysis
Transcriptome coverage	tRNA-biased	tRNA-biased; limited mRNA detection	Whole transcriptome — tRNA, mitochondrial tRNA, and exploratory mRNA D discovery
Cross-species validated	Limited	Limited	Yes — validated in human, mouse, and plant (Arabidopsis)
DUS writer assignment capability	Not supported	Limited	Yes — siRNA KD/KO experimental design integrated with D site mapping
LC-MS/MS orthogonal validation	Not routinely integrated	Not routinely integrated	Available — targeted LC-MS/MS validation of D site stoichiometry

Technical Advantages of CRACI-Seq

Single-Base Quantitative Stoichiometry

CRACI-Seq is the first D mapping method that delivers direct, quantitative readout of modification stoichiometry at each site. The T→C misincorporation frequency at a given position directly correlates with the fraction of RNA molecules carrying D at that site — enabling absolute quantification without the efficiency biases inherent to truncation-based approaches. Background correction using untreated control samples ensures accurate stoichiometry estimates even at low modification levels (10–40%).

Clustered D-Loop Resolution

tRNA D-loops frequently harbor multiple adjacent D residues (e.g., D16/D17 in the D-stem, D20/D20a/D20b in the D-loop elbow). Truncation-based methods fail at the first D, preventing detection of downstream sites within the same molecule. CRACI-Seq's read-through mechanism independently reports each D position, enabling comprehensive characterization of multi-site D modification patterns — including cis-regulatory relationships between adjacent D sites.

Integrated DUS Writer and Perturbation Analysis

Understanding D biology requires mapping not just where D occurs, but which writer enzyme installs it and how modification changes under perturbation. CRACI-Seq is compatible with siRNA KD/KO experimental designs that link specific DUS enzymes (DUS1L→D16/D17, DUS2L→D20, DUS3L→D47, DUS4L→D20a) to their target sites. Differential D analysis across treatment conditions, stress responses, and disease models reveals the regulatory dynamics of D modification.

These advantages make CRACI-Seq the method of choice for researchers investigating D modification biology — whether studying tRNA structure-function relationships, DUS enzyme specificity, mitochondrial tRNA modification, or the emerging roles of D in gene regulation and disease.

Bioinformatics and Data Analysis

Our bioinformatics pipeline for CRACI-Seq data is specifically designed to handle the unique challenges of T→C misincorporation-based D detection, including background correction, multi-mapping tRNA reads, and low-stoichiometry site identification.

Analysis Package	Content Description
Standard Analysis
1. Raw Data QC and Preprocessing	FastQC quality assessment, adapter trimming, read filtering, and rRNA removal. Alignment to reference genome (STAR, HISAT2) and transcriptome (Salmon).
2. T→C Misincorporation Calling	Per-position base composition analysis from aligned BAM files. Identification of positions with statistically significant T→C elevation relative to background. Minimum read depth and allelic fraction thresholds applied.
3. Background Correction	Untreated (no KBH₄) control samples used to establish baseline T→C misincorporation rates at each genomic position. Background-subtracted stoichiometry calculated for each candidate D site.
4. Site Annotation and Filtering	D sites annotated by RNA type (tRNA, mRNA, other ncRNA), genomic context, isodecoder family, and sequence motif. Positions with known polymorphisms or alignment artifacts excluded.
5. tRNA-Specific D Analysis	Multi-mapping read resolution using tRNA isodecoder references. Position-level D stoichiometry matrix across all detected tRNA species. Heatmap visualization of D-loop modification patterns.
Advanced Analysis
6. Differential D Analysis	Comparison of D stoichiometry between experimental groups (control vs. treatment, WT vs. KD/KO). Statistical testing with multiple hypothesis correction. Identification of significantly changing D sites.
7. DUS Writer Assignment	Integration of D site mapping with DUS enzyme perturbation data. Assignment of writer specificity based on stoichiometry changes upon individual DUS KD/KO. Cross-referencing with known DUS recognition motifs.
8. Mitochondrial tRNA D Analysis	Dedicated mt-tRNA alignment and D site calling. Detection of low-stoichiometry D sites in mitochondrial tRNAs with appropriate background control for mt-RNA-specific noise sources.
9. mRNA D Discovery (Exploratory)	Genome-wide screening for high-confidence D sites in mRNA transcripts. Stringent filters including replicate reproducibility, background subtraction, and manual review. Note: exploratory only — mRNA D sites are rare and typically low-stoichiometry.

Our bioinformatics team delivers a comprehensive analysis report with publication-ready figures, including tRNA D stoichiometry heatmaps, DUS writer assignment matrices, differential D volcano plots, and QC metrics. For orthogonal validation, our RNA Mass Spectrometry platform can provide independent confirmation of D modification levels.

Applications

CRACI-Seq is designed for research applications across tRNA biology, epitranscriptomics, and RNA modification mechanisms. The following application areas are particularly well-suited to our approach.

DUS Enzyme Biology and Specificity

Understanding which DUS writer enzyme (DUS1L–DUS4L) modifies which tRNA position is fundamental to deciphering D biology. CRACI-Seq enables systematic DUS KD/KO perturbation studies that map enzyme-site relationships and reveal functional specialization. This is particularly valuable for cancer biology, where DUS2L overexpression has been implicated in tumor progression and translation dysregulation.

Mitochondrial tRNA Modification

Mitochondrial tRNAs harbor unique D modification patterns that differ from their cytoplasmic counterparts, and defects in mt-tRNA modification are linked to mitochondrial disorders. CRACI-Seq detects D sites in mt-tRNAs — including low-stoichiometry sites (<40%) that are missed by truncation-based methods — enabling studies of mitochondrial translation regulation and modification-mediated disease mechanisms.

Stress Response and Translational Control

Dihydrouridine levels dynamically change in response to environmental stress, including heat shock, hypoxia, and nutrient deprivation. These changes are thought to modulate tRNA structure and translation efficiency. CRACI-Seq's differential D analysis capability enables quantitative tracking of D stoichiometry changes under stress conditions — providing mechanistic insight into translation reprogramming during cellular stress responses.

Cancer Epitranscriptomics

DUS enzyme dysregulation is increasingly recognized in cancer — DUS2L is upregulated in lung cancer and linked to enhanced translation of pro-tumorigenic factors, while DUS1L and DUS3L show altered expression in multiple cancer types. CRACI-Seq provides the quantitative resolution needed to test whether DUS dysregulation leads to altered D modification patterns that reprogram translation in cancer cells.

Cross-Species tRNA Modification Conservation

D modification patterns at positions D16, D17, D20, and D47 are highly conserved across vertebrates and plants. CRACI-Seq enables comparative D mapping across species (human, mouse, Arabidopsis) to investigate evolutionary conservation of D modification patterns and DUS writer specificity — supporting functional studies of D in translation regulation across model organisms.

Sample Requirements

Sample Type	Recommended Amount	Quality Requirements
Total RNA (cells or tissue)	≥1 μg total RNA	RIN ≥ 7, OD260/280 ~1.8–2.0
Small RNA enriched	≥200 ng small RNA fraction	Enriched for <200 nt fraction
Supported species	Human, Mouse, Rat, Arabidopsis	Other species upon consultation

Important Notes:

A minimum of two experimental groups (e.g., control vs. treatment) with ≥3 biological replicates per group is recommended for differential D analysis.
Untreated (no KBH₄) control samples are required for background modeling and accurate stoichiometry estimation.
For DUS writer perturbation studies: include WT, KD/KO (each DUS target), and rescue controls as appropriate for the experimental design.
For total RNA input, avoid heparin contamination which can inhibit reverse transcription and library preparation.
Non-standard species or challenging sample types (FFPE, cfRNA, biofluids): please consult with our team for feasibility assessment.

Case Study: Transcriptome-Wide Dihydrouridine Mapping by CRACI-Seq

A landmark 2025 study published in Nature Communications by Ju and colleagues (University of Chicago, Chuan He laboratory) developed and validated CRACI-Seq for quantitative, transcriptome-wide D mapping at single-base resolution — providing the first comprehensive atlas of D modification across human, mouse, and plant transcriptomes.

Dihydrouridine (D) is one of the most abundant tRNA modifications yet one of the most difficult to map quantitatively. Prior methods (D-seq, Rho-seq, AlkAniline-Seq) relied on RT truncation or chemical cleavage signals that cannot provide accurate stoichiometry and fail in densely modified D-loop regions. The authors developed CRACI-Seq to overcome these limitations, targeting quantitative single-base D mapping across the entire transcriptome.

CRACI-Seq method principle and validation

Figure 1. CRACI-Seq method principle and validation.
KBH₄ reduction of dihydrouridine (D) to tetrahydrouridine enables HIV RT with high dGTP/dNTP ratio to incorporate C opposite the reduced site, generating a T→C misincorporation signature. Validation in synthetic RNA controls demonstrates ~96% conversion efficiency and single-base quantitative resolution. Adapted from Ju et al. 2025 (CC BY 4.0).

Methods: The study used total RNA from HEK293T cells (human), mouse tissues, and Arabidopsis seedlings. CRACI-Seq was performed with KBH₄ reduction followed by HIV RT under high dGTP conditions, Illumina sequencing, and custom bioinformatic analysis for T→C misincorporation calling. siRNA KD of each DUS writer (DUS1L–DUS4L) was used for enzyme assignment. LC-MS/MS provided orthogonal validation of D site stoichiometry.

DUS writer enzyme assignment by CRACI-Seq

Figure 2. DUS writer enzyme assignment by CRACI-Seq.
siRNA knockdown of individual DUS enzymes (DUS1L–DUS4L) followed by CRACI-Seq reveals writer-specific D site assignments. DUS1L KD → reduced D16/D17, DUS2L KD → reduced D20 (including mitochondrial D sites), DUS3L KD → reduced D47, DUS4L KD → reduced D20a. Heatmap shows site-specific stoichiometry changes upon each DUS KD. Adapted from Ju et al. 2025 (CC BY 4.0).

Results: CRACI-Seq identified D at positions D16, D17, D20, D20a, D20b, and D47 across cytoplasmic tRNAs with quantitative stoichiometry (D16/D17 >70%; D20a ranging 20–100%). Novel D sites were discovered in mitochondrial tRNAs (mt-tRNA^Asn, mt-tRNA^Gln, mt-tRNA^Leu(UUR)) at moderate stoichiometries (<40%). DUS writer assignment revealed DUS1L→D16/17, DUS2L→D20, DUS3L→D47, DUS4L→D20a. Notably, D20a was found to cis-regulate D20 installation on the same tRNA. Only 8 high-confidence mRNA D sites were identified (10–40% stoichiometry), confirming that D is predominantly a tRNA modification.

FAQs — Frequently Asked Questions

- 1) What types of RNA can CRACI-Seq detect dihydrouridine in?
  - CRACI-Seq detects D modifications across the whole transcriptome. It provides robust detection in tRNAs (cytoplasmic and mitochondrial) — where D is most abundant at canonical D-loop positions (D16, D17, D20, D20a, D20b, D47). It also supports exploratory detection of D sites in mRNA transcripts, though mRNA D sites are rare and typically low-stoichiometry (10–40%), requiring stringent bioinformatic filtering and validation.
- 2) How does CRACI-Seq achieve quantitative stoichiometry?
  - The frequency of T→C misincorporation at a given position directly correlates with the fraction of RNA molecules carrying D at that site. HIV RT incorporates cytosine opposite reduced D with ~96% efficiency, and background correction using untreated (no KBH₄) control samples removes systematic noise from sequencing errors or RT misincorporation. The resulting background-subtracted T→C fraction provides a direct readout of D stoichiometry at each site.
- 3) What makes CRACI-Seq better than D-seq or Rho-seq?
  - D-seq and Rho-seq rely on RT truncation (premature termination at D sites), which has three fundamental limitations: (1) truncation efficiency does not correlate with modification fraction, precluding quantitative stoichiometry; (2) the first D site in a cluster blocks detection of downstream sites in the same molecule; (3) low truncation efficiency at certain sequence contexts results in false negatives. CRACI-Seq overcomes all three by using an internal misincorporation signal that provides quantitative, independent readout of each D position.
- 4) Can CRACI-Seq detect D in mitochondrial tRNAs?
  - Yes. CRACI-Seq has been validated for mitochondrial tRNA D detection, identifying D sites in mt-tRNA^Asn, mt-tRNA^Gln, and mt-tRNA^Leu(UUR) — including moderate-stoichiometry sites (<40%) that are below the detection limit of truncation-based methods. Dedicated mt-tRNA alignment and background correction strategies are included in our analysis pipeline.
- 5) What sample types and quality are required?
  - We recommend ≥1 μg of high-quality total RNA (RIN ≥ 7) for standard CRACI-Seq. Small RNA enriched fractions (≥200 ng) are also suitable. Supported species include human, mouse, rat, and Arabidopsis. Untreated (no KBH₄) control samples are required for background modeling. For challenging samples or non-standard species, please consult our team for feasibility assessment.
- 6) How do you handle multi-mapping tRNA reads for accurate D site assignment?
  - tRNA multi-mapping is a key challenge in D modification analysis due to highly similar isodecoder sequences. Our pipeline uses a two-pass strategy: first, reads are aligned to a comprehensive tRNA reference database with isodecoder-level resolution. Multi-mapping reads are assigned using expectation-maximization or Bayesian approaches. D stoichiometry is reported at both the isodecoder and isotype level, with confidence metrics that account for mapping ambiguity.
- 7) Can CRACI-Seq be combined with DUS KD/KO for writer assignment?
  - Yes — this is one of the key applications of CRACI-Seq. By comparing D stoichiometry profiles between WT and individual DUS KD/KO samples, we can assign each DUS enzyme to its target sites. We provide experimental design consultation for DUS perturbation studies, including appropriate controls (scramble siRNA, rescue) and replicate recommendations.
- 8) Do you provide orthogonal validation of D sites?
  - Yes. We offer targeted LC-MS/MS validation of D stoichiometry for selected tRNA sites as an add-on service. Our tRNA Modification Analysis by MS platform can independently confirm D modification levels in specific tRNA species, providing complementary evidence to the CRACI-Seq sequencing data.

References:

Ju CW, Li H, Jiang B, et al. Quantitative CRACI reveals transcriptome-wide distribution of RNA dihydrouridine at base resolution. Nat Commun. 2025;16:8863.
Lusser A, Gasser SM. Dihydrouridine: a modified nucleoside in the spotlight. Nat Rev Mol Cell Biol. 2024;25:677-678.
Bou-Nader C, Montemayor EJ, et al. Structural basis of DUSP substrate recognition and catalytic mechanism. Nature. 2024;631:428-435.
Matsuura T, et al. Human DUS1L catalyzes dihydrouridine modification at tRNA positions 16/17, and DUS1L overexpression perturbs translation. Commun Biol. 2024;7:1238.

For Research Use Only. This service is intended for exploratory and mechanistic research applications, including RNA modification profiling, tRNA biology, DUS enzyme studies, and perturbation analysis. It is not intended for clinical diagnosis, treatment selection, patient stratification, or therapeutic decision-making.

Quantitative RNA Dihydrouridine Mapping Service (CRACI-Seq)

What CRACI-Seq Measures

CRACI-Seq vs. Traditional Dihydrouridine Detection Methods