CHL1 DNA helicase plays a critical role in sister chromatid cohesion []. DDX11 is the mammalian homologue of the yeast CHL1. DDX11 is a DNA helicase involved in cellular proliferation []. In humans a second homologue has been identified, DDX12 []. DDX11 translocates on single-stranded DNA in the 5' to 3' direction in the presence of ATP and, to a lesser extent, dATP. Its unwinding activity requires a 5'-single-stranded region for helicase loading, since flush-ended duplex structures do not support unwinding []. Defects in DDX11 are the cause of Warsaw breakage syndrome (WBRS), a syndrome characterised by severe microcephaly, growth retardation, facial dysmorphism and abnormal skin pigmentation [].
A number of eukaryotic and prokaryotic proteins have been characterised [, , ]on the basis of their structural similarity. They all seem to be involved in ATP-dependent, nucleic-acid unwinding. There are two subfamilies of such proteins, the D-E-A-D-box and D-E-A-H-box families. Proteins that belong to the subfamily which have His instead of the second Asp are said to be 'D-E-A-H-box' proteins [, , ]. Proteins currently known to belong to this subfamily include yeast PRP2, PRP16, PRP22 and PRP43, involved in various ATP-requiring steps of the pre-mRNA splicing process; fission yeast prh1, which my be involved in pre-mRNA splicing; Drosophila male-less (mle) protein required in males for dosage compensation of X chromosome linked genes; yeast RAD3, a DNA helicase involved in excision repair of DNA damaged by UV light, bulky adducts or cross-linking agents; fission yeast rad15 (rhp3) and mammalian DNA excision repair protein XPD (ERCC-2); yeast CHL1 (or CTF1), which is important for chromosome transmission and normal cell cycle progression in G(2)/M; yeast TPS1, Caenorhabditis elegans hypothetical proteins C06E1.10 and K03H1.2; Poxviruses' early transcription factor 70kDa subunit which acts with RNA polymerase to initiate transcription from early gene promoters; Vaccinia virus putative helicase I8; and Escherichia coli putative RNA helicase hrpA. All these proteins share a number of conserved sequence motifs. Some of them are specific to this family while others are shared by other ATP-binding proteins or by proteins belonging to the helicases 'superfamily' [].
