One RT does not fit all: meet the next generation of FIREScript® reverse transcriptases

  • Published: 27 August 2026
Reverse transcription workflows do not all ask the same thing from an enzyme. Some require preservation of long or complex RNA templates, while others prioritize efficient RNA processing and sensitive RT-qPCR.

That is why the next generation of FIREScript® includes two reverse transcriptases with distinct RNase H profiles: FIREScript® FLEX H(-) and FIREScript® ULTRA H(+).

Both enzymes combine fast cDNA synthesis, high thermostability, broad working temperature ranges and stability designed for demanding laboratory workflows. The main question is: which is better suited for your application?

What do FIREScript® FLEX H(-) and ULTRA H(+) have in common?
Both next-generation FIREScript® reverse transcriptases were engineered for fast and robust cDNA synthesis. They show maximum activity at elevated temperatures of approximately 57–65°C, helping with the reverse transcription of GC-rich and highly structured RNA (Figure 1). They also support rapid synthesis of long cDNA, with transcripts exceeding 12 kb demonstrated in testing.

Figure (1) 
Figure 1. FIREScript® FLEX H(-) and FIREScript® ULTRA H(+) remain active across a broad temperature range, supporting reverse transcription at elevated temperatures.

Both enzymes also offer:
  • Fast cDNA synthesis in as little as 5 minutes
  • High thermostability and a broad working temperature range
  • Up to 24-hour benchtop stability due to inherent warm-start
  • Tolerance to common RT inhibitors
  • Stability TAG technology for enhanced enzyme stability
The key difference is their RNase H activity (Figure 2).

Figure 2 (1) 
Figure 2. RNase H activity comparison.
 
FLEX H(-) or ULTRA H(+)? It depends on what you need

FIREScript® FLEX H(-)

FIREScript® ULTRA H(+)

RNase H activity

Reduced

Elevated

Main advantage

Preserves RNA templates during cDNA synthesis

Efficiently processes RNA templates

Choose it when…

Full-length cDNA and template preservation are important

Sensitive and efficient RT-qPCR is the priority

Particularly useful for

Long and complex RNA workflows

Gene expression and targeted RNA detection
Choose FIREScript® FLEX H(-) when template preservation matters
FIREScript® FLEX H(-) has reduced RNase H activity, helping preserve RNA during reverse transcription and supporting accurate full-length cDNA synthesis.

This makes FLEX H(-) a strong choice when working with long or complex RNA templates or workflows where maintaining the integrity of the RNA hybrid is beneficial.

Its robustness also extends beyond the reaction itself. In testing, FLEX H(-) maintained reverse transcription performance after 30 minutes at 65°C, with only a minimal Cq shift compared with substantially larger changes for conventional reverse transcriptases.

Choose FIREScript® ULTRA H(+) when efficient RNA processing is the priority
FIREScript® ULTRA H(+) has elevated RNase H activity, enabling efficient RNA template processing and supporting high-performance RT-qPCR.

It is therefore particularly suited to workflows where sensitive RNA detection and efficient downstream qPCR are important. In comparative testing, ULTRA H(+) produced lower Cq values than the competing reverse transcriptases tested, demonstrating strong sensitivity with low-abundance RNA targets.

More flexibility coming in September!
Until now, the new FIREScript® enzymes have been available as ready-to-use kits for convenient and reproducible reverse transcription.

From September, larger kit formats will provide even more flexibility for researchers who want to optimize their own reactions. Instead of relying on a fixed all-in-one setup, users will have more freedom to adjust individual component concentrations according to their application.

This makes the FIREScript® range suitable both for researchers looking for a straightforward reverse transcription workflow and for those developing or optimizing more specialized assays.

So, which FIREScript® should you choose?
If you need reduced RNase H activity, RNA template preservation and efficient synthesis of long or complex cDNA, start with FIREScript® FLEX H(-).

If your priority is elevated RNase H activity, efficient RNA processing and sensitive RT-qPCR, choose FIREScript® ULTRA H(+).

Whichever workflow you are running, both next-generation FIREScript® reverse transcriptases bring together speed, thermostability, inhibitor tolerance and workflow stability in one platform.

Not sure which one fits your application? Request a free sample (orders@solisbiodyne.com) and test FIREScript® FLEX H(-) or FIREScript® ULTRA H(+) in your own workflow.