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- ViennaRNA RNAlib (bundled, v1.5b): ViennaRNA Package License
Background
microRNAs are short (~22 nt) non-coding RNAs that regulate gene expression by base-pairing with complementary sites in target mRNAs — most often in the 3’ untranslated region (3’UTR) — and directing those transcripts toward translational repression or degradation. Because pairing is only partial in animals and concentrated in a short 5’ “seed” of the microRNA, identifying genuine target sites from sequence alone requires a method tuned to complementarity rather than ordinary sequence identity. miRanda (Enright et al., 2003) addresses this with a two-phase algorithm. First, a Smith-Waterman local alignment scores microRNA-to-target complementarity (rewarding A:U and G:C pairs, and tolerating G:U wobble) instead of identity, with extra weighting on the microRNA’s 5’ seed region to reflect its outsized role in binding. Second, for alignments that clear a score threshold, the bundled ViennaRNA RNAlib (Hofacker et al., 1994) estimates the duplex minimum free energy (ΔG, kcal/mol). Sites that pass both the score and the energy threshold are reported as candidate target sites.Learning Resources
- hacktrackgnulinux/miranda (maintained fork) - the source repository, with the canonical command-line flag surface and build instructions.
- miRBase (Griffiths-Jones et al.) - the reference registry of published microRNA sequences and names, and the standard place to obtain the microRNA queries you scan with.
Tools
miRanda Target Scan (miranda-scan)
Scans one or more microRNA queries against one or more RNA/DNA target sequences and returns, per target, the predicted target sites — each with its complementarity score, ViennaRNA duplex free energy, 1-indexed inclusive coordinates on both strands, percent identity and similarity, and the aligned strings.API Reference
Config: MirandaConfig
Config: MirandaConfig
-sc).-en).-scale).-go).-ge).-loose when False.-noenergy when False.-trim).True is coerced to 1 and False to 0.None waits indefinitely.BaseToolOutput.approx_equal), and the seed participates in cache keys. When None, cacheable seed-sensitive tools skip cache until seeded.Applications
Use this to nominate candidate microRNA target sites in a transcript before committing to experimental validation. Typical workflows scan a small panel of microRNAs (from miRBase) against a gene’s 3’UTR to rank putative binding sites, or screen one microRNA across a set of candidate target transcripts to shortlist which are most likely regulated.Usage Tips
score_thresholdandenergy_thresholdset the sensitivity-versus-specificity trade-off. Lowering score_threshold below the default of 50 and raising energy_threshold toward 0 from the default of -20 kcal/mol both admit weaker sites and recover more candidates at the cost of more false positives; tighten them in the other direction for high-confidence calls.- Disable
strictfor more sensitivity. strict applies stringent miRNA:target duplex base-pairing heuristics by default; turning it off (-loose) is less conservative and surfaces additional, lower-confidence sites. - Disable
compute_energyfor a much faster score-only scan. compute_energy runs the ViennaRNA free-energy phase by default; turning it off skips that phase entirely (the reported energy is then 0.0), which is useful for quick large-scale complementarity sweeps where ΔG ranking is not yet needed. - All reported positions are 1-indexed and inclusive on both the target and the microRNA, matching biological coordinate conventions.
Toolkit Notes
These apply to every miRanda tool in this toolkit (miranda-scan).
- microRNA queries are user-supplied. miRanda does not ship a microRNA database; obtain query sequences from miRBase (or your own designs) and pass them as
mirna_queries. - Target sequences should be mRNAs or 3’UTRs, not whole genomes. The aligner builds a query-by-target dynamic-programming matrix, so memory scales with target length. Scan transcript-scale sequences, and use
trimto cap very long targets rather than feeding whole chromosomes. - Statistical shuffling and Z-scores are not supported in this fork. The randomization-based Z-score significance machinery is non-functional upstream and is not exposed by the wrapper; rank candidates by score and free energy instead.

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