Occurrence of five different chromosomal HMG1 proteins in various maize tissues

The nuclear HMG1 proteins of higher plants are small non-histone proteins t hat have DNA-bending activity and are considered architectural factors in c hromatin. The occurrence of the chromosomal HMG1 proteins, HMGa, HMGc1/2 an d HMGd, in various maize tissues was analyzed, and in the course of these s tudies a novel HMG1 protein, now termed HMGe, was identified. Purification and characterization of HMGe (M-r 13 655) and cloning of the corresponding cDNA revealed that it displays only moderate similarity to other members of the plant HMG1 protein family. The five maize HMG1 proteins could be detec ted in kernels, leaves, roots and suspension culture cells, indicating that these proteins can be expressed simultaneously and occur relatively ubiqui tously. However, the various HMG1 proteins are present in significantly dif ferent quantities with HMGa and HMGc1/2 being the most abundant HMG1 protei ns in all tissues tested. Furthermore, the relative amounts of the various HMG1 proteins differ among the tissues examined. The HMG1 proteins were fou nd to be relatively stable proteins in vivo, with HMGc1/2, HMGd and HMGe ha ving a half-life of ca. 50 h in cultured cells, while the half-life of the HMGa protein is ca. 65 h. Collectively, these findings are compatible with the concept that the different plant HMG1 proteins might act as general arc hitectural proteins in concert with site-specific factors in the assembly o f certain nucleoprotein structures involved in various biological processes .