  The mechanism and the region of generation of variable continuum emission are
poorly understood for radio-loud AGN because of a complexity of the nuclear
region. High-resolution radio VLBI (very long baseline interferometry)
observations allow zooming into a subparsec-scale region of the jet in the
radio-loud galaxy 3C 390.3. We combined the radio VLBI and the optical data
covering the time period of 14 years to look for a link between optical flares
and parsec-scale jet. We identify two stationary and nine moving radio features
in the innermost subparsec-scale region of the jet. All nine ejections are
associated with optical flares. We found a significant correlation (at a
confidence level of $>99.99%$) between the ejected jet components and optical
continuum flares. The epochs at which the moving knots pass through the
location of a stationary radio feature and the optical light curve reaches the
maximum are correlated. The radio events follow the maxima of optical flares
with the mean time delay of $0.10\pm0.04$ years. This correlation can be
understood if the variable optical continuum emission is generated in the
innermost part of the jet. A possible mechanism of the energy release is the
ejection of knots of high-energy electrons that are accelerated in the jet flow
and generate flares of synchrotron continuum emission in the wide range of
frequencies from radio to X-ray bands. In this scenario, the beamed optical
continuum emission from the jet and counterjet ionizes a gas in a
subrelativistic outflow surrounding the jet, which results in a formation of
two outflowing conical regions with broad emission lines (in addition to the
conventional broad line region around the central nucleus).
