The present invention provides double stranded compositions wherein each
strand is modified to have a motif defined by positioning of
.beta.-D-ribonucleosides and sugar modified nucleosides. More
particularly, the present compositions comprise one strand having an
alternating motif and another strand having a hemimer motif, a blockmer
motif, a fully modified motif or a positionally modified motif. At least
one of the strands has complementarity to a nucleic acid target. The
compositions are useful for targeting selected nucleic acid molecules and
modulating the expression of one or more genes. In preferred embodiments
the compositions of the present invention hybridize to a portion of a
target RNA resulting in loss of normal function of the target RNA. The
present invention also provides methods for modulating gene expression.