The present invention provides double stranded compositions wherein the first strand is modified to have a particular motif and the second strand is modified a selected motif. The motifs are defined by positioning of differentially modified nucleosides wherein at least the sugar moieties are different. More particularly, the present compositions comprise an antisense strand that is modified to have a positional/full motif and the sense strand is modified to have an alternating motif, a hemimer motif, a blockmer motif, a gapped motif, a positional motif, a positional/full motif or a fully modified motif. Each strand further comprises one or more phosphorothioate internucleoside linkage. 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.