  The high redshift GPS quasar PKS 0858-279 exhibits the following properties
which make the source unusual. Our RATAN-600 monitoring of 1-22 GHz spectrum
has detected broad-band radio variability with high amplitude and relatively
short time scale. In the same time, the milliarcsecond scale structure observed
in a snapshot VLBA survey turned out to be very resolved which is not expected
from the fast flux density variations. We performed 1.4-22 GHz VLBA
observations of this quasar in 2005-2007. It has revealed a core-jet
morphology. A high Doppler factor delta is suggested for the jet, its nature is
discussed in this report on the basis of the multi-frequency VLBA and RATAN
data collected. Synchrotron self-absorption was confirmed to be dominating at
low frequencies, the magnetic field strength of the dominating jet feature is
estimated of an order of 0.1*delta mG.
