  A resonance search has been made in the K0s p and K0s pbar invariant-mass
spectrum measured with the ZEUS detector at HERA using an integrated luminosity
of 121 pb-1. The search was performed in the central rapidity region of
inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318
GeV for exchanged photon virtuality, Q2, above 1 GeV2. Recent results from
fixed-target experiments give evidence for a narrow baryon resonance decaying
to K+ n and K0s p, interpreted as a pentaquark. The results presented here
support the existence of such state, with a mass of
1521.5+/-1.5(stat.)^{+2.8}_{-1.7}(syst.) MeV and a Gaussian width consistent
with the experimental resolution of 2 MeV. The signal is visible at high Q2
and, for Q2>20 GeV2, contains 221+/-48 events. The probability of a similar
signal anywhere in the range 1500-1560 MeV arising from fluctuations of the
background is below 6x10^{-5}.
