Jr. Wisniewski et U. Grossbach, STRUCTURAL AND FUNCTIONAL-PROPERTIES OF LINKER HISTONES AND HIGH-MOBILITY GROUP PROTEINS IN POLYTENE CHROMOSOMES, The International journal of developmental biology, 40(1), 1996, pp. 177-187
Variants of histone H1 and high mobility group (HMG) proteins and thei
r genes in Dipteran insects are being studied in our laboratory and ha
ve revealed differential properties of DNA binding and intrachromosoma
l distribution. One of the H1 variants of Chironomus is found only in
a minority of polytene chromosome bands and differs from the other H1
proteins of the same organism by genomic organization and by an insert
ed structural motif, the KAPKAP repeat, that is present also in single
H1 variants of other, evolutionarily remote organisms. NH2-terminal p
eptides containing the KAPKAP repeat were found in vitro to interact w
ith DNA, whereas no DNA interaction was observed with the homologous p
eptide of another H1 variant that does not contain the inserted KAPKAP
repeat. We assume that H1 variants containing the KAP motif may inter
act with a stretch of linker DNA and package chromatin more tightly th
an other H1 variants. A large series of antibodies directed against di
fferent sites in all regions of the H1 molecule is being applied in st
udying the sites of interaction of the H1 molecule with other molecule
s in interphase chromatin in terms of antibody epitope accessibility.
A search for insect proteins that share properties of the mammalian HM
G proteins resulted in isolation and sequencing of two different HMG1
proteins and an HMGI protein. The HMG1 proteins of the midge, Chironom
us tentans, show a differential distribution in chromosomes. The more
abundant cHMG1a protein appears uniformly distributed, whereas the les
s abundant cHMG1b protein could be localized only in chromosomal puffs
. This strongly indicates that these highly similar proteins have diff
erent functions in chromatin. The Chironomus HMGI protein and the intr
on/exon organization of its gene were found to be very similar to huma
n HMGI/Y proteins that are highly abundant in rapidly proliferating ce
lls. Common properties of HMG1 and HMGI proteins include high affinity
interaction with AT-rich DNA, irregular DNA structures, and the capac
ity to bend DNA. These properties suggest that the HMG proteins may ha
ve an architectural role in assembling different types of chromatin.