DNA-dependent ATPase and ATP-dependent DNA helicase that participates in various functions in genomic stability, including DNA replication, DNA repair and heterochromatin organization as well as in ribosomal RNA synthesis. Its double-stranded DNA helicase activity requires either a minimal 5'-single-stranded tail length of approximately 15 nt (flap substrates) or 10 nt length single-stranded gapped DNA substrates of a partial duplex DNA structure for helicase loading and translocation along DNA in a 5' to 3' direction. The helicase activity is capable of displacing duplex regions up to 100 bp, which can be extended up to 500 bp by the replication protein A (RPA) or the cohesion CTF18-replication factor C (Ctf18-RFC) complex activities. Shows also ATPase- and helicase activities on substrates that mimic key DNA intermediates of replication, repair and homologous recombination reactions, including forked duplex, anti-parallel G-quadruplex and three-stranded D-loop DNA molecules. Plays a role in DNA double-strand break (DSB) repair at the DNA replication fork during DNA replication recovery from DNA damage. Recruited with TIMELESS factor upon DNA-replication stress response at DNA replication fork to preserve replication fork progression, and hence ensure DNA replication fidelity (By similarity). Cooperates also with TIMELESS factor during DNA replication to regulate proper sister chromatid cohesion and mitotic chromosome segregation (PubMed:17611414). Stimulates 5'-single-stranded DNA flap endonuclease activity of FEN1 in an ATP- and helicase-independent manner; and hence it may contribute in Okazaki fragment processing at DNA replication fork during lagging strand DNA synthesis. Its ability to function at DNA replication fork is modulated by its binding to long non-coding RNA (lncRNA) cohesion regulator non-coding RNA DDX11-AS1/CONCR, which is able to increase both DDX11 ATPase activity and binding to DNA replicating regions (By similarity). Plays also a role in heterochromatin organization (PubMed:21854770). Involved in rRNA transcription activation through binding to active hypomethylated rDNA gene loci by recruiting UBTF and the RNA polymerase Pol I transcriptional machinery (By similarity). Plays a role in embryonic development and prevention of aneuploidy (PubMed:17611414). Involved in melanoma cell proliferation and survival. Associates with chromatin at DNA replication fork regions. Binds to single- and double-stranded DNAs (By similarity). ATP + H2O = ADP + H(+) + phosphate Binds 1 [4Fe-4S] cluster. Associates with the CTF18-RFC complex. Associates with a cohesin complex composed of RAD21, SMC1 proteins and SMC3. Interacts with CHTF18. Interacts with DSCC1. Interacts with FEN1; this interaction is direct and increases flap endonuclease activity of FEN1. Interacts with PCNA. Interacts with POLR1A and UBTF. Interacts with RAD21, SMC1 proteins and SMC3. Interacts with RFC2. Interacts with TIMELESS; this interaction increases recruitment of both proteins onto chromatin in response to replication stress induction by hydroxyurea. During the early stages of mitosis, localizes to condensed chromatin and is released from the chromatin with progression to metaphase. Also localizes to the spindle poles throughout mitosis and at the midbody at later stages of mitosis (metaphase to telophase). In interphase, colocalizes with nucleolin in the nucleolus. Embryonic death at 10.5 dpc (PubMed:17611414). Embryos are smaller in size, malformed and exhibit sparse cellularity in comparison to normal or heterozygous litter mates (PubMed:17611414). Show inability to form a proper embryonic placenta. Display high incidence of cell aneuploidy due to abnormal chromosomal segregation (PubMed:17611414). Show abnormal formation and localization of heterochromatin (PubMed:21854770). Belongs to the DEAD box helicase family. DEAH subfamily. DDX11/CHL1 sub-subfamily. Aberrant splicing.