Variability in Arabidopsis thaliana chromosomal high-mobility-group-1-like proteins

The vertebrate high‐mobility‐group (HMG) protein HMG1 is an abundant non‐histone protein which is considered as an architectural element in chromatin. In the monocotyledonous plant maize, four different HMG1‐like proteins (HMGa, HMGc1/2, HMGd) have been identified, whereas other eukaryotes usually express only two different proteins of this type. We have examined here the HMG1‐like proteins of the dicotyledonous plant Arabidopsis thaliana. The isolation and analysis of cDNAs encoding five different so far uncharacterised HMG1‐like proteins (now termed HMGα, HMGβ1/2, HMGγ, HMGδ) from Arabidopsis indicates that the expression of multiple HMG1‐like proteins is a general feature of (higher) plants. The Arabidopsis HMG1‐like proteins contain an HMG domain as a common feature, but outside this conserved DNA‐binding motif the amino acid sequences are significantly different indicating that this protein family displays a greater structural variability in plants than in other eukaryotes. The five HMG1‐like proteins were expressed in Escherichia coli and purified. They bind with somewhat different affinity to linear double‐stranded DNA. The recognition of DNA structure is evident from their preferential interaction with DNA minicircles relative to linear DNA. Reverse‐transcribed PCR suggested that the five HMG1‐like genes are simultaneously expressed in Arabidopsis leaves and suspension culture cells.