Ribozymes containing 2'-fluoro- and 2'-amino-modified pyrimidine nucle
osides in combination with terminal phosphorothioate linkages were tar
geted against HTLV-I fax RNA. In oder to examine the activity of such
chemically modified ribozymes in the nuclear environment, they were in
cubated with nuclei of a Tax-transformed mouse fibroblast cell line. R
ibozyme cleavage of tax RNA was analyzed by the RNase protection assay
. Comparison of the cleavage of tax RNA isolated nuclei with that of t
ax RNA present in nuclei suspension revealed a 30 times more efficient
cleavage of the latter one. Pre-treatment with proteinase K and SDS a
bolished the enhancement of the ribozyme-mediated RNA cleavage. Cataly
tically inactive ribozymes did not yield any cleavage products. These
results demonstrate an augmenting effect of nuclear proteins on the ri
bozyme-mediated RNA cleavage.