UBA1 and proximal spinal muscular atrophy: To estimate the degree of sequence conservation in Uba1 and help elicit critical domain sequences surrounding the altered residues in patients with XL-SMA, the complete amino acid sequences of Uba1 enzymes were aligned and analyzed from a wide range of species using the Multalin program 5.4.1 (Corpet, 1988).Saccharomyces cerevisiae (yeast),Danio rerio (zebrafish) and five well-studied mammalian Uba1 Multalin aligments are shown inFigure 1A.