  In the present paper we demonstrate that there exists a fully microscopic
shell-model counterpart of the Bohr-Mottelson model by embedding the latter in
the microscopic shell-model theory of atomic nucleus within the framework of
the recently proposed fully microscopic proton-neutron symplectic model (PNSM).
For this purpose, another shell-model coupling scheme of the PNSM is considered
in which the basis states are classified by the algebraic structure $SU(1,1)
\otimes SO(6)$. It is shown that the configuration space of the PNSM contains a
six-dimensional subspace that is closely related to the configuration space of
the generalized quadrupole-monopole Bohr-Mottelson model and its dynamics
splits into radial and orbital motions. The group $SO(6)$ acting in this space,
in contrast, e.g., to popular IBM, contains an $SU(3)$ subgroup which allows to
introduce microscopic shell-model counterparts of the exactly solvable limits
of the Bohr-Mottelson model that closely parallel the relationship of the
original Wilets-Jean and rotor models. The Wilets-Jean-type dynamics in the
present approach, in contrast to the original collective model formulation, is
governed by the microscopic shell-model intrinsic structure of the symplectic
bandhead which defines the relevant Pauli allowed $SO(6)$, and hence $SU(3)$,
subrepresentations. The original Wilets-Jean dynamics of the generalized
Bohr-Mottelson model is recovered for the case of closed-shell nuclei, for
which the symplectic bandhead structure is trivially reduced to the scalar or
equivalent to it irreducible representation.
