  We study the relation between the VLBA (Very Long Baseline Array) radio
emission at 15 GHz and the optical nuclear emission at 5100 A for a sample of
233 core-dominated AGN with relativistic jets. For 181 quasars, there is a
significant positive correlation between optical nuclear emission and total
radio (VLBA) emission of unresolved cores (on milliarcsecond scales) of the jet
at 15 GHz. Optical continuum emission correlates with radio emission of the jet
for 31 BL Lacs. These correlations confirm that the radio and optical emission
are beamed and originate at sub-parsec scales in the innermost part of the jet
in quasars, while they are generated in the parsec-scale jet in BL Lacs. These
results are in agreement with that reported earlier by Arshakian et al. 2010
for a sample of 135 AGN.
