  Variational calculations for s-shell hypernuclei are performed by explicitly
including $\Sigma$ degrees of freedom. Four sets of YN interactions (SC97d(S),
SC97e(S), SC97f(S) and SC89(S)) are used. The bound-state solution of
$_\Lambda^5$He is obtained and a large energy expectation value of the tensor
$\Lambda N-\Sigma N$ transition part is found. The internal energy of the
$^4$He subsystem is strongly affected by the presence of a $\Lambda$ particle
with the strong tensor $\Lambda N-\Sigma N$ transition potential.
