Pseudouridine: BID-seq and BACS-seq

01What this article answers

BID-seq and BACS-seq are antibody-free, base-resolution methods for pseudouridine (Ψ). Both exploit the behavior of Ψ under bisulfite chemistry, and both return a position and a level rather than an enriched region.

The difference is what the sequencer reads. BID-seq follows bisulfite-induced deletion: Ψ resists the reagent, stays unconverted, and produces a deletion signature during reverse transcription. BACS-seq uses controlled bisulfite conversion: Ψ is protected and read as a distinct signature while the unmodified bases are converted, which is what places the quantification on an absolute scale.

So the choice is less about which method finds more and more about which signal a group is set up to analyze.

02Two signals from one chemistry

Both routes start from the same property of the modified base and separate at the point where the treated RNA is read.

	BID-seq	BACS-seq
Basis	Bisulfite-induced deletion sequencing	Controlled bisulfite conversion
What the sequencer reads	A deletion signature: Ψ resists the reagent and is lost from the read at that position	A signature of its own: Ψ is protected while unmodified bases are converted
Level	A modification level follows from the conversion-based readout	The protected fraction gives an absolute modification level
Antibody	None in the workflow	None in the workflow
Transcript scopes	mRNA, or mRNA together with lncRNA	mRNA, or mRNA together with lncRNA
Extra option	—	A Ψ and inosine version profiles both marks from one library

Because neither route enriches anything before sequencing, the signal at a position comes from the chemistry itself. That matters for interpretation: nothing here is scaled by how much material a capture step happened to pull down.

The inosine option is worth noting for projects that already have a reason to read both marks. The Ψ and inosine version of BACS-seq profiles the two from a single library rather than requiring the work to be split.

03How to choose

Both methods are base-resolved and antibody-free, and both are offered in the same two transcript scopes, so the decision turns on the signal and on the analyses built around it.

Which signal does the group already work with? A deletion-based readout and a protected-signature readout arrive as different data, and the analysis pipeline follows from that.
Is an absolute level needed? Where levels are to be compared directly across sites, samples or conditions, the route whose readout is described as absolute is the natural choice.
Is inosine in scope as well? If the study also needs inosine, the combined Ψ and inosine version of BACS-seq covers both marks from one library.
What is the transcript scope? Both routes support mRNA alone, or mRNA together with long non-coding RNA, in one experiment.

04Limits and common misreadings

Both routes are single-base methods. Neither reports an enriched region, and neither returns a peak to be read as a position.
Ψ-RIP-Seq is a different level of resolution. That workflow enriches pseudouridine-carrying fragments with an antibody and reports a transcript-level profile; it is not interchangeable with a base-level call.
A deletion is not an absence. In BID-seq the missing base at a position is the signature, so it has to be read as a call rather than as a gap in the data.
Level is not effect. A modification level reports how much of a position carries the mark, which is a different statement from what that mark does to the transcript.

05Where to go next

Both pseudouridine methods have full service pages, and the antibody-based route for the same mark is described on the RIP line.

Ψ · 01

Pseudouridine (Ψ) Seq (BID-seq)

Bisulfite-induced deletion signatures mark Ψ positions across the transcriptome.

Site-leveldeletion signal Ψ · 02

Pseudouridine (Ψ) Seq (BACS-seq)

Controlled bisulfite conversion reports Ψ from a protected signature.

Absolutelevel Ψ & I

Ψ and Inosine Seq (BACS-seq)

Pseudouridine and inosine profiled from a single BACS-seq library.

Site-leveltwo marks Ψ-RIP

Pseudouridine (Ψ) Seq (Ψ-RIP-Seq)

Antibody enrichment of pseudouridine-containing fragments, reported as a profile.

Regionenrichment

06FAQ

What makes pseudouridine visible in a bisulfite-based assay?

Its behavior under the reagent. In BID-seq it resists the reaction and leaves a deletion signature; in BACS-seq it is protected under controlled conditions and read as a signature of its own while the unmodified bases convert. The difference matters because the two signatures arrive as different data, and the analysis pipeline follows from that.

Do both methods come with a modification level?

Yes. Both readouts are conversion-based and report a level at the called position rather than only evidence that the mark is present there. Since neither route enriches anything before sequencing, that level comes from the chemistry itself and is not scaled by how much material a capture step happened to pull down.

Is an antibody used in either route?

No. Neither workflow contains an immunoprecipitation step, so neither result is shaped by antibody binding preferences. That is also why the readout is a position with a level rather than an enriched region: what the sequencer sees comes from the chemistry acting on pseudouridine, not from where a capture reagent bound.

Can pseudouridine and inosine be read together?

Yes, with the combined Ψ and inosine version of BACS-seq, which profiles both marks from a single library. It is worth considering where a study already has a reason to read inosine, since keeping the two marks in one library avoids splitting the same material across two workflows.