The conserved domain database (CDD) was performed to analyze domains of AtGUS, and there were sugar-binding domain, immunoglobulin-like beta-sandwich domain, and TIM barrel domains in it which all belonged to glycoside hydrolase family (GHF) 2. GHF 2 comprised b-galactosidase (EC 3.2.1.23), bmannosidase (EC 3.2.1.25), and b-glucuronidase (EC 3.2.1.31), so the phylogenetic tree was constructed according to it (Figure 3) . It showed that the gene cloned was a b-glucuronidase gene named AtGUS (Genbank accession No. JF894133), which was found very similar to PGUS(Genbank accession No. EU095019) from P. purpurogenum Li-3 and AuGUS (Genbank accession No. JN247805) from A. ustus Li-62, especially in the sugar-binding, immunoglobulin-like beta-sandwich, and TIM barrel domain ( Table 1 ). The obvious difference among them lied in the non-conservative sequence of the C-terminal behind the TIM barrel domain which may result in the difference enzymatic properties. Therefore, the 1-1,776 bp segment, named Atgus(-3t), was amplified in the 