RECQL4 is not critical for firing of human DNA replication origins

RECQL4, a member of the RecQ helicase family, plays a role in maintaining genomic stability, but its precise function remains unclear. The N-terminus of RECQL4 has similarity to Sld2, a protein required for the firing of DNA replication origins in budding yeast. Consistent with this sequence similarity, Xenopus RECQL4 has been implicated in initiating DNA replication in oocyte extracts. To determine whether human RECQL4 is required for firing of DNA replication origins, we generated cells in which both RECQL4 alleles were targeted, resulting in either lack of protein expression (Knock-Out) or expression of a full-length, mutant protein lacking helicase activity (Helicase Dead). Surprisingly, both the RECQL4 Knock-Out and Helicase Dead cells were viable and exhibited essentially identical origin firing profiles as the parental cells. Analysis of the rate of fork progression revealed normal rates in the RECQL4 Knock Out cells, but decreased rates in the RECQL4 inactive cells. Thus, while budding yeast Sld2 is required for DNA replication origin firing, our evidence suggest that human RECQL4 has assumed a role in the regulation of replication fork progression. EdUseq data of RECQL4 WT and mutant cells (CRISPR KOs bearing frameshifts to the N-terminal (fsN)or helicase (fsN) domain of the protein and helicase inactive mutants (KM)), under normal (NE) and overexpression (OE) conditions of ectopic CCNE, addressing the origin firing profile (EdUseq), fork progression (EdUseq_RXX) and Mitotic DNA synthesis profiles (MiDASseq)