| SREBPs belongs to the transcription factor family of basic helix-loop-helix leucine-zipper (bHLH-zip). It is the key nuclear transcriptional factor in eukaryotic cell which regulates lipid metabolism. This paper acquired the partial mRNA sequence of SREBP-2 gene of two breed geese: Landes goose (Anser anser) and Tianfu meat goose (Anser cygnoides). For this reason, the bHLH-zip motif of SREBP-2 were obtained, and what we studied was mainly build on this motif. Using chicken genome as a model, we investigated the classification and evolution of HLH transcription factors.Sequences were submitted to Genbank and the accession number were EF579754 and EF579755 respectively. The result of alignment showed that the similarity of two sequences, both of which contained a typical bHLH-zip motif, were up to 100%.The bHLH-zip motif of SREBP-2 in different species were highly conserved. Compared with other species, the result of alianment showed that there were 7 amino acid polymorphic sites at 5, 14, 23, 25, 28, 32, 54 position. Moreover, when compared with other families of HLH transcription factor, it was surprising that the bHLH-zip motif of SREBP-2 gene did not contain P, which deserves further investigation.HLH proteins were classified by the sequce of bHLH-zip motif of SREBP-2. The result shows that there were 18 kinds of related domains, which were closely related to the biological function of HLH, and maintained independency in evolution. We suggested that there is 'domain shuffling' mechanism involved in genome evolution.The study about chicken genome showed that HLH transcription factor contains 28 groups of protein families, which can be divided into A, B, C, D and E classes. In evolution, A is close to D, and C is relatively close to E. It was supposed that A, B, C and D might be evolved from B.Compared with the standard of mammals' classification, class F was absent in the chicken genome. Moreover, the families and number of HLH transcription factors in chicken genome were less.
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