Volume 272, Number 45,
Issue of November 7, 1997
pp. 28289-28295
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
The C-terminal Subdomain Makes an Important Contribution to
the DNA Binding Activity of the Pax-3 Paired Domain
(Received for publication, July 25, 1997)
Kyle J.
Vogan
and
Philippe
Gros
From the Department of Biochemistry, McGill University, Montreal,
Quebec H3G 1Y6, Canada
The recognition of DNA targets by Pax-3 is
achieved through the coordinate use of two distinct
helix-turn-helix-based DNA-binding modules: a paired domain, composed
of two structurally independent subdomains joined by a short linker,
and a paired-type homeodomain. In mouse, the activity of the Pax-3
paired domain is modulated by an alternative splicing event in the
paired domain linker region that generates isoforms
(Q+ and Q
) with distinct C-terminal
subdomain-mediated DNA-binding properties. In this study, we have used
derivatives of a classical high affinity paired domain binding site
(CD19-2/A) to derive an improved consensus recognition sequence for the
Pax-3 C-terminal subdomain. This new consensus differs at six out of
eight positions from the C-terminal subdomain recognition motif present
in the parent CD19-2/A sequence, and includes a 5
-TT-3
dinucleotide
at base pairs 15 and 16 that promotes high affinity binding by both
Pax-3 isoforms. However, with a less favorable guanine at position 15, only the Q
isoform retains high affinity binding to this
sequence, suggesting that this alternative splicing event might serve
to stabilize binding to suboptimal recognition sequences. Finally,
mutagenic analysis of the linker demonstrates that both the sequence
and the spacing in this region contribute to the enhanced DNA-binding properties of the Pax-3/Q
isoform. Altogether, our
studies establish a clear role for the Pax-3 C-terminal subdomain in
DNA recognition and, thus, provide insights into an important mechanism
by which Pax proteins achieve distinct target specificities.