  We present an update of 3C 273's database hosted by the ISDC, completed with
data from radio to gamma-ray observations over the last 10 years. We use this
large data set to study the multiwavelength properties of this
quasar,especially focussing on its variability behaviour. We study the
amplitude of the variations and the maximum variability time scales across the
broad-band spectrum and correlate the light curves in different bands,
specifically with the X-rays, to search for possible connections between the
emission at different energies. 3C 273 shows variability at all frequencies,
with amplitudes and time scales strongly depending on the energy and being the
signatures of the different emission mechanisms. The variability properties of
the X-ray band imply the presence of either two separate components (possibly a
Seyfert-like and a blazar-like) or at least two parameters with distinct timing
properties to account for the X-ray emission below and above ~20 keV. The
dominant hard X-ray emission is most probably not due to electrons accelerated
by the shock waves in the jet as their variability does not correlate with the
flaring millimeter emission, but seems to be associated to long-timescale
variations in the optical. This optical component is consistent with being
optically thin synchrotron radiation from the base of the jet and the hard
X-rays would be produced through inverse Compton processes (SSC and/or EC) by
the same electron population. We show evidence that this synchrotron component
extends from the optical to the near-infrared domain, where it is blended by
emission of heated dust that we find to be located within about 1 light-year
from the ultraviolet source.
