  We perform evolutionary calculations of binary stars to find progenitors of
systems with parameters similar to the recurrent nova U Sco. We show that a U
Sco-type system may be formed starting with an initial binary system which has
a low-mass carbon-oxygen white dwarf as an accretor. Since the evolutionary
stage of the secondary is not well known, we calculate sequences with
hydrogen-rich and helium-rich secondaries. The evolution of the binary may be
divided into several observable stages as: classical nova, supersoft X-ray
source with stable hydrogen shell burning, or strong wind phase. It culminates
in the formation of a massive white dwarf near the Chandrasekhar mass limit. We
follow the chemical evolution of the secondary as well as of the matter lost
from the system, and we show that observed $^{12}$C/$^{13}$C and N/C ratios may
give some information about the nature of the binary.
