Genome-wide base composition bias curves in Illumina reads from PCR-free human DNA libraries. ( a ) The GC-bias curves from libraries (in duplicate) produced by the immobilized enzyme method (IM-1 and IM-2 in blue), for end repair for 30 min at 20 °C and 3′ A-tailing at 37 °C in contrast to the data from the libraries generated by the soluble enzyme method, with 3′ A-tailing at 65 °C, using enzyme mixture PKT (PKT-1 and PKT-2 in purple). ( b ) The GC-bias data of the immobilized enzyme method compared to the data from the duplicate libraries generated by Illumina TruSeq DNA PCR-free LT Library Preparation Kit (Illumina), Kapa Hyper Prep Kit (Kapa) or NEBNext Ultra II DNA Library Prep Kit for Illumina (Ultra) according to the protocols of the manufacturers. The Illumina protocol carries out end repair for 30 min at 30 °C and 3′ A-tailing for 30 min at 37 °C, followed by incubation at 70 °C for 5 min, and includes a clean-up and size selection step between end repair and 3′ A-tailing. The Kapa Hyper and NEBNext Ultra workflows include an enzyme mixture to perform end repair for 30 min at 20 °C, followed by 3′ A-tailing for 30 min at 65 °C.
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