IDENTIFICATION OF CDNA CLONES ENCODING HMG-2, A MAJOR PROTEIN OF THE MEXICAN AXOLOTL HYDROCORTISONE-SENSITIVE THYMOCYTES

We have identified and analyzed cDNA clones encoding a major 26 kDa pr otein of the HMG1-2 family which is abundant in the cytoplasm and nucl eus of axolotl hydrocortisone-sensitive thymocytes. The axolotl HMG2 p rotein is very similar to proteins belonging to the HMG1-2 family, fro m teleost fish to mammals. All the molecular features of the HMG1-2 pr oteins are conserved, including the high proportion of basic and aroma tic residues, and the characteristic acidic C-terminus tail. The S'-un translated region of the HMG2 axolotl cDNA is also similar to the avia n and mammalian HMG2 3'-UT sequences, suggesting that some selective e vents have acted at the DNA level to conserve this region, which could be important in the differential expression of the HMG1 and HMG2 gene s. The axolotl HMG2 protein contains the two well conserved HMG boxes which are thought to be the DNA-binding domains of the molecule. Axolo tl thymocytes and spleen cells contain almost identical amounts of HMG 2 mRNAs but HMG2 polypeptide is undetectable in spleen cells using ant i-26 kDa antibodies. The reason for the accumulation of HMG1-2 molecul es in vertebrate hydrocortisone-sensitive thymocytes is discussed, as well as their possible role in apoptosis.