Volume 272, Number 47,
Issue of November 21, 1997
pp. 29904-29910
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
High Mobility Group I Proteins Interfere with the Homeodomains
Binding to DNA
(Received for publication, April 25, 1997, and in revised form, August 1, 1997)
Paola
Arlotta
,
Alessandra
Rustighi
,
Fiamma
Mantovani
,
Guidalberto
Manfioletti
,
Vincenzo
Giancotti
,
Gianluca
Tell
§
and
Giuseppe
Damante
§
From the Dipartimento di Biochimica, Biofisica e Chimica delle
Macromolecole, Università di Trieste, 34100 Trieste, Italy and
the § Dipartimento di Scienze e Tecnologie Biomediche,
Università di Udine, 33100 Udine, Italy
Homeodomains (HDs) constitute the DNA binding
domain of several transcription factors that control cell
differentiation and development in a wide variety of organisms. Most
HDs recognize sequences that contain a 5
-TAAT-3
core motif. However,
the DNA binding specificity of HD-containing proteins does not solely determine their biological effects, and other molecular mechanisms should be responsible for their ultimate functional activity. Interference by other factors in the HD/DNA interaction could be one of
the processes by which HD-containing proteins achieve the functional
complexity required for their effects on the expression of target
genes.
Using gel-retardation assay, we demonstrate that two members of the
high mobility group I (HMGI) family of nuclear proteins (HMGI-C and
HMGY) can bind to a subset of HD target sequences and inhibit HDs from
binding to the same sequences. The inhibition of the HD/DNA interaction
occurs while incubating HMGI-C with DNA either before or after the
addition of the HD.
The reduced half-life of the HD·DNA complex in the presence of
HMGI-C, and the shift observed in the CD spectra recorded upon HMGI-C
binding to DNA, strongly suggest that structural modifications of the
DNA are responsible for the inhibition of the HD·DNA complex formation. Moreover, by co-transfection experiments we provide evidence
that this inhibition can occur also in vivo.
The data reported here would suggest that HMGI proteins may be
potential regulators of the function of HD-containing proteins and that
they are able to interfere with the access of the HD to their target
genes.