Jr. Wisniewski et al., REGION OF INSECT HIGH-MOBILITY GROUP (HMG)-1 PROTEIN HOMOLOGOUS TO HELIX-2 OF THE RAT HMG1-B BOX IS IN CLOSE CONTACT WITH DNA, The Journal of biological chemistry, 269(46), 1994, pp. 29261-29264
The dipteran insects Chironomus and Drosophila have high mobility grou
p (HMG) 1 proteins that are similar to mammalian HMG1 but contain one
instead of two HMG1 boxes. The interaction of the Chironomus HMG1 prot
eins cHMG1a and cHMG1b with double-stranded and four-way junction DNA
was analyzed by investigating the accessibility of defined sequences o
f the HMG1 box to specific antibodies within the DNA-protein complex i
n vitro. Antibody epitopes located in the three helices and in the tur
n between helices 1 and 2 of the HMG1 box were identified on a membran
e onto which 90 decapeptides with overlapping sequences spanning the e
ntire sequence of cHMG1a had been bound. Monospecific antibodies direc
ted against selected epitopes were purified from a polyclonal antiseru
m by affinity chromatography. Helices 1 and 3 as well as the turn betw
een helices 1 and 2 were found 60 be accessible to antibodies in the c
omplex. In contrast, antibodies recognizing an epitope on putative hel
ix 2 of cHMG1a and cHMG1b were unable to produce supershifts on gels o
f the DNA-protein complexes with both DNAs. These data suggest that he
lix 2 of the HMG1 box of proteins cHMG1a and cHMG1b is essentially res
ponsible for contacts with DNA.