4 DIFFERENTLY CHROMATIN-ASSOCIATED MAIZE HMG DOMAIN PROTEINS MODULATEDNA-STRUCTURE AND ACT AS ARCHITECTURAL ELEMENTS IN NUCLEOPROTEIN COMPLEXES

In contrast to other eukaryotes which usually express two closely rela ted HMG1-like proteins, plant cells have multiple relatively variable proteins of this type. A systematic analysis of the DNA-binding proper ties of four chromosomal HMG domain proteins from maize revealed that they bind linear DNA with similar affinity. HMGa, HMGc1/2 and HMGd spe cifically recognise diverse DNA structures such as DNA mini-circles an d supercoiled DNA. They induce DNA-bending, and constrain negative sup erhelical turns in DNA. In the presence of DNA, the HMG domain protein s can self-associate, whereas they are monomeric in solution. The maiz e HMG1-like proteins have the ability to facilitate the formation of n ucleoprotein structures to different extents, since they can efficient ly replace a bacterial chromatin-associated protein required for the s ite-specific P-mediated recombination. a variable function of the HMG1 -like proteins is indicated by their differential association with mai ze chromatin, as judged by their 'extractability' from chromatin with spermine and ethidium bromide. Collectively, these findings suggest th at the various plant chromosomal HMG domain proteins could be adapted to act in different nucleoprotein structures in vivo.