A4 beta-galactosidase middle domain: a type 1 glutamine amidotransferase (GATase1)-like domain. A4 beta-galactosidase middle domain: a type 1 glutamine amidotransferase (GATase1)-like domain. This group includes proteins similar to beta-galactosidase from Thermus thermophilus. Beta-Galactosidase hydrolyzes the beta-1,4-D-galactosidic linkage of lactose, as well as those of related chromogens, o-nitrophenyl-beta-D-galactopyranoside (ONP-Gal) and 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-gal). This A4 beta-galactosidase middle domain lacks the catalytic triad of typical GATase1 domains. The reactive Cys residue found in the sharp turn between a beta strand and an alpha helix termed the nucleophile elbow in typical GATase1 domains is not conserved in this group.
DEXXQ-box helicase domain of SETX. The RNA/DNA helicase senataxin (SETX) plays a role in transcription, neurogenesis, and antiviral response. SEXT is an R-loop-associated protein that is thought to function as an RNA/DNA helicase. R-loops consist of RNA/DNA hybrids, formed during transcription when nascent RNA hybridizes to the DNA template strand, displacing the non-template DNA strand. Mutations in SETX are linked to two neurodegenerative disorders: ataxia with oculomotor apraxia type 2 (AOA2) and amyotrophic lateral sclerosis type 4 (ALS4). S. cerevisiae homolog splicing endonuclease 1 (Sen1) is an exclusively nuclear protein, important for nucleolar organization. S. cerevisiae Sen1 and its ortholog, the Schizosaccharomyces pombe Sen1, share conserved domains and belong to the family I class of helicases. Both proteins translocate 5' to 3' and unwind both DNA and RNA duplexes and also RNA/DNA hybrids in vitro. SETX is a member of the DEAD-like helicase superfamily, a diverse family of proteins involved in ATP-dependent RNA or DNA unwinding. This domain contains the ATP-binding region.
